Display panel, data processor, and method for manufacturing display panel

ABSTRACT

Provided is a novel display panel that is highly convenient or reliable, a novel data processor that is highly convenient or reliable, or a method for manufacturing a novel display panel that is highly convenient or reliable. The display panel includes a pixel and a terminal electrically connected to the pixel. The pixel includes a first insulating film, a first contact portion in a first opening provided in the first insulating film, a pixel circuit electrically connected to the first contact portion, a second contact portion electrically connected to the pixel circuit, a first display element electrically connected to the first contact portion, and a second display element electrically connected to the second contact portion. The first insulating film includes a region lying between the first display element and the second display element. The terminal includes a surface at which contact with other component can be made.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.15/290,073, filed Oct. 11, 2016, now allowed, which is a divisional ofU.S. application Ser. No. 15/092,221, filed Apr. 6, 2016, now abandoned,which claims the benefit of foreign priority applications filed in Japanas Serial No. 2015-081519 on Apr. 13, 2015, Serial No. 2015-115638 onJun. 8, 2015, and Serial No. 2015-150202 on Jul. 30, 2015, all of whichare incorporated by reference.

TECHNICAL FIELD

One embodiment of the present invention relates to a display panel, adata processor, a method for manufacturing a display panel, or asemiconductor device.

Note that one embodiment of the present invention is not limited to theabove technical field. The technical field of one embodiment of theinvention disclosed in this specification and the like relates to anobject, a method, or a manufacturing method. Another embodiment of thepresent invention relates to a process, a machine, manufacture, or acomposition of matter. Specifically, examples of the technical field ofone embodiment of the present invention disclosed in this specificationinclude a semiconductor device, a display device, a light-emittingdevice, a power storage device, a memory device, a method for drivingany of them, and a method for manufacturing any of them.

BACKGROUND ART

A liquid crystal display device in which a light-condensing means and apixel electrode are provided on one side of a substrate and a regiontransmitting visible light in the pixel electrode is provided to overlapwith an optical axis of the light-condensing means is known. Inaddition, a liquid crystal display device which uses an anisotropiclight-condensing means having a light-condensing direction X and anon-light-condensing direction Y, where the non-light-condensingdirection Y corresponds to a longitudinal direction of a regiontransmitting visible light in the pixel electrode is known (PatentDocument 1).

REFERENCE Patent Document

-   [Patent Document 1] Japanese Published Patent Application No.    2011-191750

DISCLOSURE OF INVENTION

One object of one embodiment of the present invention is to provide anovel display panel that is highly convenient or reliable. Anotherobject of one embodiment of the present invention is to provide a noveldata processor that is highly convenient or reliable. Another object ofone embodiment of the present invention is to provide a method formanufacturing a novel display panel that is highly convenient orreliable. Another object of one embodiment of the present invention isto provide a novel display panel, a novel data processor, a method formanufacturing a novel display panel, or a novel semiconductor device.

The descriptions of these objects do not disturb the existence of otherobjects. Note that one embodiment of the present invention does notnecessarily achieve all the objects. Other objects will be apparent fromand can be derived from the descriptions of the specification, thedrawings, the claims, and the like.

Means for Solving the Problems

(1) One embodiment of the present invention is a display panel includinga pixel and a terminal.

The pixel includes a first insulating film, a first contact in a firstopening provided in the first insulating film, a pixel circuitelectrically connected to the first contact, a second contactelectrically connected to the pixel circuit, a first display elementelectrically connected to the first contact, and a second displayelement electrically connected to the second contact.

The first insulating film includes a region lying between the firstdisplay element and the second display element. The first displayelement includes a reflective film. The reflective film reflectsincident light and includes a second opening. The first display elementis configured to control the intensity of the reflected light.

The second display element includes a region overlapping with the secondopening. The region overlapping with the second opening emits lighttoward the second opening.

The terminal is electrically connected to the pixel circuit and includesa surface at which contact with other component can be made.

(2) One embodiment of the present invention is the display panel inwhich the pixel circuit includes a switching element.

The display panel according to one embodiment of the present inventionincludes the pixel and the terminal electrically connected to the pixel.The pixel includes the first insulating film, the first contact in thefirst opening provided in the first insulating film, the pixel circuitelectrically connected to the first contact, the second contactelectrically connected to the pixel circuit, the first display elementelectrically connected to the first contact, and the second displayelement electrically connected to the second contact. The firstinsulating film includes the region lying between the first displayelement and the second display element. The terminal includes thesurface at which contact with other component can be made.

With the structure, the first display element and the second displayelement between which the first insulating film is provided can bedriven using the pixel circuit connected to the terminal, for example.Thus, a novel display panel which is highly convenient or reliable canbe provided.

(3) One embodiment of the present invention is the display panel inwhich the pixel circuit includes a transistor capable of suppressingoff-state current more than a transistor in which amorphous silicon isused as a semiconductor.

Since the pixel circuit of the display panel according to one embodimentof the present invention includes the transistor capable of suppressingoff-state current, the frequency of supplying a selection signal to thepixel circuit can be reduced while flickers with display performance issuppressed. Thus, a novel display panel with reduced power consumptionwhich is highly convenient or reliable can be provided.

(4) One embodiment of the present invention is the display panel inwhich the first display element includes a layer containing a liquidcrystal material and first and second conductive films. The first andsecond conductive films are provided so that the alignment of the liquidcrystal material can be controlled. The first conductive film iselectrically connected to the first contact.

(5) One embodiment of the present invention is the display panel inwhich the second display element includes a third conductive film, afourth conductive film including a region overlapping with the thirdconductive film, and a layer containing a light-emitting organiccompound between the third conductive film and the fourth conductivefilm. The third conductive film is electrically connected to the secondcontact and transmits light.

In the display panel, which is one embodiment of the present invention,a reflective liquid crystal element and an organic EL element are usedas the first display element and the second display element,respectively.

Owing to the structure, in a bright place, external light and thereflective liquid crystal element are utilized to perform display, whilein a dark place, light emitted from the organic EL element is utilizedto perform display. In a dim place, external light and light emittedfrom the organic EL element are utilized to perform display. Thus, anovel display panel capable of performing display with high visibility,a novel display panel with reduced power consumption, or a novel displaypanel highly convenient or reliable can be provided.

(6) One embodiment of the present invention is the display panel inwhich the first display element is configured to reflect external lightand in which the ratio of the total area of the second opening providedin the reflective film to that of a portion of the reflective film otherthan the second opening is more than or equal to 0.052 and less than orequal to 0.6. The area of the second opening is larger than or equal to3 μm² and smaller than or equal to 25 μm².

The display panel, which is one embodiment of the present invention,includes the second element which is configured to reflect externallight and one or more of the openings. The area of one opening is largerthan or equal to 3 μm² and smaller than or equal to 25 μm². The ratio ofthe total area of the opening to that of the reflective film other thanthe opening is more than or equal to 0.052 and less than or equal to 0.6

Thus, irregular alignment of the liquid crystal material can be avoided.In a bright place, display can be performed utilizing external light. Ina dark place, display can be performed utilizing light emitted from theorganic EL element. Thus, a novel display panel capable of performingdisplay with high visibility, a novel display panel with reduced powerconsumption, or a novel display panel highly convenient or reliable canbe provided.

(7) One embodiment of the present invention is the display panel inwhich the reflective film includes a region embedded in the firstinsulating film and a region not covered by the first insulating film.

Since the display panel, which is one embodiment of the presentinvention, includes the reflective film which is composed of the exposedregion and the region embedded in the first insulating film, a step atthe edge of the reflective film can be minimized to reduce thepossibility of alignment defects due to the step. In addition, thesurface serving as the contact of the terminal can be exposed. Thus, anovel display panel which is highly convenient or reliable can beprovided.

(8) One embodiment of the present invention is the display panel inwhich the surface at which contact with other component can be madefaces the same direction as a surface of the reflective film whichreflects external light used for performing display. The terminalincludes a region embedded in the first insulating film and a region notcovered by the second insulating film.

The display panel according to one embodiment of the present inventionincludes the terminal including the region embedded in the firstinsulating film and the region not covered by the second insulatingfilm. Accordingly, the surface of the terminal at which contact withother component can be made can be exposed. Thus, such a novel displaypanel which is highly convenient or reliable can be provided.

(9) One embodiment of the present invention is the display panel inwhich the pixel includes a second insulating film. The second insulatingfilm includes a region that is provided such that the reflective film issandwiched between the region and the first insulating film, and aregion that covers the reflective film.

(10) One embodiment of the present invention is a data processorincluding an arithmetic device and an input/output device.

The arithmetic device is configured to receive positional informationand to supply image information and control information.

The input/output device is configured to supply the positionalinformation and to receive the image information and the controlinformation. The input/output device includes a display portion thatdisplays the image information and an input portion that supplies thepositional information.

The display portion includes the above-mentioned display panel. Theinput portion is configured to detect the position of a pointer and tosupply the positional information based on the position.

The arithmetic device is configured to determine the moving speed of thepointer in accordance with the positional information and to determinethe contrast or brightness of the image information in accordance withthe moving speed of the pointer.

The data processor of one embodiment of the present invention includesthe input/output device that supplies the positional information andreceives the image information and the arithmetic device. The arithmeticdevice receives the positional information and supplies the imageinformation and determines the contrast or brightness of the imageinformation in accordance with the moving speed of the pointer. With thestructure, eyestrain on a user which might be caused by scrolling theimage information can be reduced, that is, eye-friendly display can beachieved. Thus, a novel data processor that is highly convenient orreliable can be provided.

(11) One embodiment of the present invention is the data processor inwhich the input portion includes at least one of a keyboard, a hardwarebutton, a pointing device, a touch sensor, an illuminance sensor, animaging device, an audio input device, a viewpoint input device, and apose detection device.

Thus, power consumption can be reduced and excellent visibility can beensured even in a bright place. Thus, a novel data processor that ishighly convenient or reliable can be provided.

(12) One embodiment of the present invention is a manufacturing methodof the display panel including the following 11 steps.

A step 1 is for forming the first insulating film over a substrate foruse in manufacturing processes.

A step 2 is for forming the reflective film and the terminal.

A step 3 is for forming the second insulating film covering thereflective film and the terminal.

A step 4 is for forming the first contact electrically connected to thereflective film and the third contact electrically connected to theterminal.

A step 5 is for forming the pixel circuit electrically connected to thefirst contact and the third contact.

A step 6 is for forming the second contact electrically connected to thepixel circuit.

A step 7 is for forming the second display element electricallyconnected to the second contact.

A step 8 is for stacking a substrate.

A step 9 is for separating the substrate for use in manufacturingprocesses.

A step 10 is for removing the first insulating film to expose thereflective film and the terminal.

A step 11 is for forming the first display element.

The manufacturing method of the display panel, which is one embodimentof the present invention, includes the step for separating the substratefor use in manufacturing processes and the step for removing the firstinsulating film to expose the reflective film and the terminal.Accordingly, a step at the edge of the reflective film can be minimizedto reduce the possibility of alignment defects due to the step. Inaddition, the surface of the terminal at which contact with othercomponents is made can be exposed. A manufacturing method of a noveldisplay panel that is highly convenient or reliable can be thusprovided.

Although the block diagram attached to this specification showscomponents classified by their functions in independent blocks, it isdifficult to classify actual components according to their functionscompletely and it is possible for one component to have a plurality offunctions.

In this specification, the terms “source” and “drain” of a transistorinterchange with each other depending on the polarity of the transistoror the levels of potentials applied to the terminals. In general, in ann-channel transistor, a terminal to which a lower potential is appliedis called a source, and a terminal to which a higher potential isapplied is called a drain. Further, in a p-channel transistor, aterminal to which a lower potential is applied is called a drain, and aterminal to which a higher potential is applied is called a source. Inthis specification, although connection relation of the transistor isdescribed assuming that the source and the drain are fixed in some casesfor convenience, actually, the names of the source and the draininterchange with each other depending on the relation of the potentials.

Note that in this specification, a “source” of a transistor means asource region that is part of a semiconductor film functioning as anactive layer or a source electrode connected to the semiconductor film.Similarly, a “drain” of the transistor means a drain region that is partof the semiconductor film or a drain electrode connected to thesemiconductor film. A “gate” means a gate electrode.

Note that in this specification, a state in which transistors areconnected to each other in series means, for example, a state in whichonly one of a source and a drain of a first transistor is connected toonly one of a source and a drain of a second transistor. In addition, astate in which transistors are connected parallel to each other means astate in which one of a source and a drain of a first transistor isconnected to one of a source and a drain of a second transistor and theother of the source and the drain of the first transistor is connectedto the other of the source and the drain of the second transistor.

In this specification, the term “connection” means electrical connectionand corresponds to a state where current, voltage, or a potential can besupplied or transmitted. Accordingly, a connection state means not onlya state of direct connection but also a state of indirect connectionthrough a circuit element such as a wiring, a resistor, a diode, or atransistor that allows current, voltage, or a potential to be suppliedor transmitted.

In this specification, even when different components are connected toeach other in a circuit diagram, there is actually a case where oneconductive film has functions of a plurality of components such as acase where part of a wiring serves as an electrode. The term“connection” also means such a case where one conductive film hasfunctions of a plurality of components.

In addition, in this specification, one of a first electrode and asecond electrode of a transistor refers to a source electrode and theother refers to a drain electrode.

One embodiment of the present invention provides a novel display panelthat is highly convenient or reliable, a novel information processingdevice that is highly convenient or reliable, a method for manufacturinga novel display panel that is highly convenient or reliable, a noveldisplay panel, a novel information processing device, a method formanufacturing a display panel, or a novel semiconductor device.

Note that the description of these effects does not disturb theexistence of other effects. One embodiment of the present invention doesnot necessarily achieve all the effects listed above. Other effects willbe apparent from and can be derived from the description of thespecification, the drawings, the claims, and the like.

BRIEF DESCRIPTION OF DRAWINGS

FIGS. 1A to 1C are top views and a circuit diagram illustrating thestructure of a display panel according to one embodiment of the presentinvention.

FIGS. 2A to 2C are cross-sectional views illustrating the structure of adisplay panel according to one embodiment of the present invention.

FIGS. 3A and 3B are cross-sectional views illustrating the structure ofa terminal of a display panel according to one embodiment of the presentinvention.

FIGS. 4A and 4B are cross-sectional views illustrating the structure ofa terminal of a display panel according to one embodiment of the presentinvention.

FIG. 5 is a cross-sectional view illustrating the structure of aterminal of a display panel according to one embodiment of the presentinvention.

FIGS. 6A and 6B are top views illustrating the structure of a pixelaccording to one embodiment of the present invention.

FIG. 7 is a cross-sectional view illustrating the structure of a displaypanel according to one embodiment of the present invention.

FIGS. 8A to 8C are cross-sectional views illustrating the structure of adisplay panel according to one embodiment of the present invention.

FIGS. 9A to 9D are circuit diagrams illustrating the structure of adisplay portion according to one embodiment of the present invention.

FIG. 10 is a cross-sectional view illustrating the structure of adisplay panel according to one embodiment of the present invention.

FIG. 11 is a cross-sectional view illustrating the structure of adisplay panel according to one embodiment of the present invention.

FIG. 12 is a flow chart illustrating a method for manufacturing adisplay panel according to one embodiment of the present invention.

FIG. 13 illustrates a method for manufacturing a display panel accordingto one embodiment of the present invention.

FIG. 14 illustrates a method for manufacturing a display panel accordingto one embodiment of the present invention.

FIG. 15 illustrates a method for manufacturing a display panel accordingto one embodiment of the present invention.

FIG. 16 illustrates a method for manufacturing a display panel accordingto one embodiment of the present invention.

FIG. 17 illustrates a method for manufacturing a display panel accordingto one embodiment of the present invention.

FIG. 18 illustrates a method for manufacturing a display panel accordingto one embodiment of the present invention.

FIG. 19 illustrates a method for manufacturing a display panel accordingto one embodiment of the present invention.

FIGS. 20A to 20D illustrate the structure of a transistor according toone embodiment of the present invention.

FIGS. 21A to 21C illustrate the structure of a transistor according toone embodiment of the present invention.

FIG. 22 illustrates the structure of an input/output device according toone embodiment of the present invention.

FIGS. 23A and 23B are a block diagram and a projection view illustratingthe structure of an information processor according to one embodiment ofthe present invention.

FIGS. 24A to 24C are block diagrams and a circuit diagram illustratingthe structure of a display portion according to one embodiment of thepresent invention.

FIGS. 25A and 25B are flow charts illustrating a program according toone embodiment of the present invention.

FIG. 26 schematically illustrates image information according to oneembodiment of the present invention.

FIGS. 27A to 27C are a cross-sectional view and circuit diagramsillustrating the structure of a semiconductor device according to oneembodiment of the present invention.

FIG. 28 is a block diagram illustrating the structure of a CPU accordingto one embodiment of the present invention.

FIG. 29 is a circuit diagram illustrating the structure of a storageelement according to one embodiment of the present invention.

FIGS. 30A to 30H illustrate the structures of electronic devicesaccording to one embodiment of the present invention.

FIGS. 31A1 to 31C are images for showing the display quality of adisplay panel according to one example of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

The display panel according to one embodiment of the present inventionincludes the pixel and the terminal electrically connected to the pixel.The pixel includes the second insulating film, the first contact in theopening provided in the second insulating film, the pixel circuitelectrically connected to the first contact, the second contactelectrically connected to the pixel circuit, the first display elementelectrically connected to the first contact, and the second displayelement electrically connected to the second contact. The secondinsulating film includes the region lying between the first displayelement and the second display element. The terminal includes thesurface at which contact with other component can be made.

With the structure, the first display element and the second displayelement between which the second insulating film is provided can bedriven using the pixel circuit connected to the terminal, for example.Thus, a novel display panel which is highly convenient or reliable canbe provided.

Embodiments will be described in detail with reference to drawings. Notethat the present invention is not limited to the description below, andit is easily understood by those skilled in the art that various changesand modifications can be made without departing from the spirit andscope of the present invention. Accordingly, the present inventionshould not be interpreted as being limited to the content of theembodiments below. Note that in the structures of the inventiondescribed below, the same portions or portions having similar functionsare denoted by the same reference numerals in different drawings, anddescription of such portions is not repeated.

Embodiment 1

In this embodiment, the structure of a display panel of one embodimentof the present invention will be described with reference to FIGS. 1A to1C and FIGS. 2A to 2C.

FIGS. 1A to 1C illustrate the structure of the display panel of oneembodiment of the present invention. FIG. 1A is a top or bottom view ofa display panel 700, 700B, or 700C of one embodiment of the presentinvention. FIG. 1B is a top view of a pixel 702(i,j) illustrated in FIG.1B. Note that in this specification, an integral variable of 1 or moremay be used for reference numerals. For example, “(p)” where p is anintegral variable of 1 or more may be used for part of a referencenumeral that specifies any one of components (p components in maximum).For another example, “(m, n)” where m and n are each an integralvariable of 1 or more may be used for part of a reference numeral thatspecifies any one of components (m×n components in maximum).

FIGS. 2A to 2C illustrate the structure of the display panel of oneembodiment of the present invention. FIG. 2A is a cross-sectional viewof the display panel 700 taken along the section lines X1-X2, X3-X4, andX5-X6 in FIG. 1A. FIG. 2B is a cross-sectional view of a transistor M inFIG. 2A. FIG. 2C is a cross-sectional view of a transistor MD in FIG.2A.

<Structure Example 1 of Display Panel>

The display panel 700 described in this embodiment includes the pixel702(i,j) and a substrate 770 (see FIG. 1A).

The substrate 770 includes a region overlapping with the pixel 702(i,j)(see FIG. 2A).

The pixel 702(i,j) includes a first display element 750, a seconddisplay element 550 having a region overlapping with the first displayelement 750, and a functional layer 520 between the first displayelement 750 and the second display element 550.

The functional layer 520 includes a first contact 704C electricallyconnected to the first display element 750, a second contact 504Celectrically connected to the second display element 550, and a pixelcircuit 730(i,j) electrically connected to the first contact 704C andthe second contact 504C (see FIG. 1C and FIG. 2A).

The first display element 750 includes a reflective film reflectingincident light and has a function of controlling the ratio of reflectionto incident light. For example, a first conductive film 751 can serve asthe reflective film (see FIG. 2A).

The reflective film includes an opening 751H. The second display element550 has a region overlapping with the opening 751H. In the case of usingthe first conductive film 751 as the reflective film, the firstconductive film 751 has the opening 751H.

The region of the second display element 550 overlapping with theopening 751H has a function of emitting light toward the opening 751H.Note that light emitted from the second display element 550 is extractedfrom a display surface of the display panel 700 through the opening751H.

The pixel circuit 730(i,j) of the display panel 700 includes a switchingelement, such as a switch SW1 or a switch SW2 (see FIG. 1C).

The display panel 700 includes the first display element 750, the seconddisplay element 550 having the region overlapping with the first displayelement 750, the first contact 704C electrically connected to the firstdisplay element 750, the second contact 504C electrically connected tothe second display element 550, and the pixel circuit 730(i,j)electrically connected to the first contact 704C and the second contact504C.

With the structure, the first and second display elements can be drivenby the pixel circuit which can be formed in the same process and can beincluded in the functional layer. Thus, a novel display panel which ishighly convenient or reliable can be provided.

The pixel circuit 730(i,j) of the display panel 700 also includes atransistor that can be used as a switch and can suppress off-statecurrent more than a transistor including an amorphous silicon as asemiconductor (see FIG. 1C).

Since the pixel circuit 730(i,j) of the display panel 700 includes sucha transistor capable of suppressing off-state current, the frequency ofsupplying a selection signal to the pixel circuit can be reduced whilesuppressing flickers with display. Thus, a novel display panel withreduced power consumption and which is highly convenient or reliable canbe provided.

The first display element 750 of the display panel 700 includes a layer753 containing a liquid crystal material, the first conductive film 751,and the second conductive film 752. The first conductive film 751 andthe second conductive film 752 are provided to control the alignment ofthe liquid crystal material. Electrical connection with the firstconductive film 751 is made at the first contact 704C.

The second display element 550 of the display panel 700 includes a thirdconductive film 551, a fourth conductive film 552 having a regionoverlapping with the third conductive film 551, and a layer 553containing a light-emitting organic compound between the thirdconductive film 551 and the fourth conductive film 552. The thirdconductive film 551 is electrically connected to the second contact 504Cand transmits light.

The display panel 700 includes a reflective liquid crystal element andan organic EL element which are respectively used as the first displayelement 750 and the second display element 550.

Owing to the structure, in a bright place, external light and thereflective liquid crystal element are utilized to perform display, whilein a dark place, light emitted from the organic EL element is utilizedto perform display. Thus, a novel display panel highly convenient orreliable can be provided.

The second display element 550 preferably has a function of reflectingexternal light. For example, a material reflecting visible light can beused for the fourth conductive film 552.

The ratio of the total area of openings including the opening 751H inthe reflective film to that of a portion of the reflective film otherthan the openings is more than or equal to 0.052 and less than or equalto 0.6. The area of one opening 751H is larger than or equal to 3 μm²and smaller than or equal to 25 μm². Note that in the case of using thefirst conductive film 751 as the reflective film, the ratio of the totalarea of openings including the opening 751H in the first conductive film751 to that of a portion of the first conductive film 751 other than theopenings is more than or equal to 0.052 and less than or equal to 0.6(see FIG. 1B).

When the area of a pixel is assumed to be 1, the area of the reflectivefilm can be more than or equal to 0.5 and less than or equal to 0.95 ofthe area of the pixel. Furthermore, the area of the opening 751H can bemore than or equal to 0.052 and less than or equal to 0.3 of the area ofthe pixel.

Owing to the structure, in a bright place, external light and thereflective liquid crystal element are utilized to perform display, whilein a dark place, light emitted from the organic EL element is utilizedto perform display. In a dim place, external light and light emittedfrom the organic EL element are utilized to perform display. Inaddition, the size of the opening is small enough to perform displaywhile avoiding irregular alignment of liquid crystal elements. Thus, anovel display panel highly convenient or reliable can be provided.

The pixel 702(i,j) of the display panel 700 includes an insulating film501A covering the first conductive film 751 and an insulating film 501Bbetween the first conductive film 751 and the pixel circuit 730(i,j).

The first conductive film 751 is provided between the insulating film501A and the insulating film 501B and is embedded in the insulating film501B.

Since the display panel 700 includes the first conductive film 751embedded in the insulating film 501B, a step at the edge of the firstconductive film can be minimized to reduce the possibility of alignmentdefects due to the step. Thus, a novel display panel highly convenientor reliable can be provided.

Note that the display panel 700 can include one or a plurality ofpixels. For example, n pixels 702(i,j) can be arranged in a rowdirection and m pixels 702(i,j) can be arranged in a column directionwhich intersects with the row direction. Note that i is an integergreater than or equal to 1 and less than or equal to m, j is an integergreater than or equal to 1 and less than or equal to n, and each of mand n is an integer greater than or equal to 1.

In addition, the display panel 700 can include scan lines G1(i) andG2(i) electrically connected to pixels 702(i,1) to 702(i,n) arranged inthe row direction (see FIG. 1C).

In addition, the display panel 700 can include a signal line 5(j)electrically connected to pixels 702(1,j) to 702(m,j) arranged in thecolumn direction.

In addition, the pixel 702(i,j) of the display panel 700 includes acoloring film CF1 having a region overlapping with the first displayelement 750, a light blocking film BM having an opening in a regionoverlapping with the first display element 750, and an insulating film771 between the coloring film CF1 or the blocking film BM and the layer753 containing a liquid crystal material (see FIG. 2A). Owing to theinsulating film 771, unevenness due to the thickness of the coloringfilm CF1 can be avoided. Alternatively, impurities can be prevented frombeing diffused from the light blocking film BM, the coloring film CF1,or the like to the layer 753 containing a liquid crystal material

The display panel 700 includes an alignment film AF2 between thesubstrate 770 and the layer 753 containing a liquid crystal material andan alignment film AF1 between the layer 753 containing a liquid crystalmaterial and the insulating film 501A.

In the display panel 700, the layer 753 containing a liquid crystalmaterial is surrounded by the substrate 770, the insulating film 501A,and a sealant 705. The sealant 705 has a function of bonding thesubstrate 770 and the insulating film 501A.

The display panel 700 includes a structure KB1 for the space between thesubstrate 770 and the insulating film 501A.

The display panel 700 includes an optical film 770P having a regionoverlapping with the pixel 702(i,j). In the display panel 700, thesubstrate 770 is provided between the optical film 770P and the layer753 containing a liquid crystal material.

The display panel 700 includes the functional layer 520. The functionallayer 520 includes the insulating film 501A, the insulating film 501B,an insulating film 501C, an insulating film 521B, an insulating film521A, and an insulating film 528.

The insulating film 501B and the insulating film 501C each have anopening where the first contact 704C is provided. Although theinsulating film 501C is stacked over the insulating film 501B in thisembodiment, the insulating film 501C may be omitted.

The insulating film 521B has a region overlapping with the insulatingfilm 501C.

The insulating film 521A lies between the insulating film 501C and theinsulating film 521B.

The insulating film 521A has an opening where the second contact 504C isprovided.

The insulating film 528 has an opening where the second display element550 is provided.

In the display panel 700, a coloring film CF2 lies between the seconddisplay element 550 and the opening 751H in the reflective film.

The display panel 700 includes a substrate 570 having a regionoverlapping with the functional layer 520, and a bonding layer 505bonding the functional layer 520 and the substrate 570.

In the display panel 700, the second display element 550 lies betweenthe functional layer 520 and the substrate 570.

The display panel 700 includes a structure KB2 between the functionallayer 520 and the substrate 570 to provide a space therebetween.

The display panel 700 includes a driver circuit GD. The driver circuitGD includes the transistor MD, for example (see FIG. 1A and FIG. 2A).The driver circuit GD has a function of supplying a selection signal tothe scan line G1(i) or the scan line G2(i), for example.

The display panel 700 includes a wiring 511 and a terminal 519 which areelectrically connected to the pixel circuit 730(0. The display panel 700can include a wiring ANO, a wiring VCOM1, and a wiring VCOM2 (see FIG.1C and FIG. 2A).

Note that a flexible printed circuit board FPC1 can be electricallyconnected to the terminal 519 using a conductive material film ACF1. Forexample, the display panel 700 can be electrically connected to a drivercircuit SD using the conductive material film ACF1.

The display panel 700 can include a terminal 719 (see FIG. 4A). Theterminal 719 is electrically connected to the second conductive film752, for example. Note that a flexible printed circuit board FPC2 can beelectrically connected to the terminal 719 using a conductive materialfilm ACF2. Note that a material of the terminal 519 can be used for theterminal 719 and a material of the conductive material film ACF1 can beused for the conductive material film ACF2.

The display panel 700 can include a conductive member electricallyconnecting the second conductive film 752 and the terminal 519 (see FIG.4B or FIG. 5). For example, a conductive particle can be used as theconductive member.

Note that the driver circuit SD supplies an image signal in accordancewith image information.

Components of the display panel 700 will be described below. Note thatthe components cannot be clearly distinguished and one unit serves asanother unit or include part of another unit in some cases.

For example, in the case where a conductive film reflecting visiblelight is used as the first conductive film 751, the first conductivefilm 751 can be used as a reflective film: the first conductive film 751serves as the reflective film, and the reflective film serves as thefirst conductive film 751.

<Structure>

The display panel 700 includes the substrate 570, the substrate 770, thewiring 511, and the terminal 519.

The display panel 700 includes the sealant 705, the bonding layer 505,the structure KB1, and the structure KB2.

The display panel 700 includes the pixel 702(i,j), the first displayelement 750, and the second display element 550.

The display panel 700 includes the first conductive film 751, the secondconductive film 752, the layer 753 containing a liquid crystal material,the opening 751H, and the reflective film.

The display panel 700 includes the third conductive film 551, the fourthconductive film 552, and the layer 553 containing a light-emittingorganic compound.

The display panel 700 includes the functional layer 520, the pixelcircuit 730(i,j), the first contact 704C, and the second contact 504C.

The display panel 700 includes the switching element, the transistor M,the transistor MD, the insulating film 501A, the insulating film 501B,the insulating film 501C, the insulating film 521A, the insulating film521B, and the insulating film 528.

The display panel 700 includes the coloring film CF1, the coloring filmCF2, the light-blocking film BM, the insulating film 771, the alignmentfilm AF1, the alignment film AF2, and the optical film 770P.

The display panel 700 includes the driver circuit GD and the drivercircuit SD.

<<Substrate 570>>

The substrate 570 can be formed using a material having heat resistancehigh enough to withstand heat treatment in the manufacturing process.

For example, a large-sized glass substrate having any of the followingsizes can be used as the substrate 570: the 6th generation (1500 mm×1850mm), the 7th generation (1870 mm×2200 mm), the 8th generation (2200mm×2400 mm), the 9th generation (2400 mm×2800 mm), and the 10thgeneration (2950 mm×3400 mm). Thus, a large-sized display device can bemanufactured.

For the substrate 570, an organic material, an inorganic material, acomposite material of an organic material and an inorganic material, orthe like can be used. For example, an inorganic material such as glass,ceramic, or a metal can be used for the substrate 570.

Specifically, non-alkali glass, soda-lime glass, potash glass, crystalglass, quartz, sapphire, or the like can be used for the substrate 570.Specifically, a material containing an inorganic oxide, an inorganicnitride, an inorganic oxynitride, or the like can be used for thesubstrate 570. For example, a material containing silicon oxide, siliconnitride, silicon oxynitride, aluminum oxide, or the like can be used forthe substrate 570. Stainless steel, aluminum, or the like can be usedfor the substrate 570.

For example, a single crystal semiconductor substrate or apolycrystalline semiconductor substrate of silicon or silicon carbide, acompound semiconductor substrate of silicon germanium, or an SOIsubstrate can be used as the substrate 570. Thus, a semiconductorelement can be formed over the substrate 570.

For example, a composite material, such as a resin film to which a metalplate, a thin glass plate, or an inorganic film is bonded can be usedfor the substrate 570. For example, a composite material formed bydispersing a fibrous or particulate metal, glass, inorganic material, orthe like into a resin film can be used for the substrate 570. Forexample, a composite material formed by dispersing a fibrous orparticulate resin, organic material, or the like into an inorganicmaterial can be used for the substrate 570.

A single-layer material or a stacked-layer material in which a pluralityof layers are stacked can be used for the substrate 570. For example, astacked-layer material in which a base, an insulating film that preventsdiffusion of impurities contained in the base, and the like are stackedcan be used for the substrate 570. Specifically, a stacked-layermaterial in which glass and one or a plurality of films that preventdiffusion of impurities contained in the glass and that are selectedfrom a silicon oxide layer, a silicon nitride layer, a siliconoxynitride layer, and the like are stacked can be used for the substrate570. Alternatively, a stacked-layer material in which a resin and a filmfor preventing diffusion of impurities that penetrate the resin, such asa silicon oxide film, a silicon nitride film, and a silicon oxynitridefilm are stacked can be used for the substrate 570.

Specifically, a material including polyester, polyolefin, polyamide(e.g., nylon or aramid), polyimide, polycarbonate, an acrylic resin, aurethane resin, an epoxy resin, a resin having a siloxane bond, such asa silicone resin, or the like can be used for the substrate 570.Alternatively, a film, a plate, a stacked body, or the like whichcontains any one or more of the resins can be used for the substrate570.

Specifically, polyethylene terephthalate (PET), polyethylene naphthalate(PEN), polyethersulfone (PES), acrylic, or the like can be used for thesubstrate 570.

Alternatively, paper, wood, or the like can be used for the substrate570.

For example, a flexible substrate can be used as the substrate 570.

Note that a transistor, a capacitor, or the like can be directly formedon the substrate. Alternatively, a transistor, a capacitor, or the likecan be formed over a substrate for use in manufacturing processes havingheat resistance and can be transferred to another substrate, in whichcase heat treatment temperature in the process for fabricating thesubstrate 570 included in the display panel of one embodiment of thepresent invention can be reduced, for example. Thus, a transistor, acapacitor, or the like can be formed over a flexible substrate.

<<Substrate 770>>

A light-transmitting material can be used for the substrate 770. Forexample, a material that can be used for the substrate 570 can be usedfor the substrate 770.

<<Wiring 511 and Terminal 519>>

A conductive material can be used for the wiring 511 or the terminal519.

For example, an inorganic conductive material, an organic conductivematerial, or the like can be used for the wiring 511 or the terminal519.

Specifically, the wiring 511 or the terminal 519 can be formed of ametal, conductive ceramic, or the like. For example, a metal elementselected from aluminum, gold, platinum, silver, copper, chromium,tantalum, titanium, molybdenum, tungsten, nickel, iron, cobalt,palladium, and manganese can be used for the wiring 511 or the terminal519. Alternatively, an alloy including any of the above-described metalelements, or the like can be used for wiring 511 or the terminal 519. Inparticular, an alloy of copper and manganese is preferably used inmicrofabrication using wet etching.

Specifically, the following structures can be used for the wiring 511 orthe terminal 519: a two-layer structure in which a titanium film isstacked over an aluminum film, a two-layer structure in which a titaniumfilm is stacked over a titanium nitride film, a two-layer structure inwhich a tungsten film is stacked over a titanium nitride film, atwo-layer structure in which a tungsten film is stacked over a tantalumnitride film or a tungsten nitride film, a three-layer structure inwhich a titanium film, an aluminum film, and a titanium film are stackedin this order, or the like.

For example, a conductive oxide, such as indium oxide, indium tin oxide,indium zinc oxide, zinc oxide, or zinc oxide to which gallium is added,can be used for the wiring 511 or the terminal 519.

Specifically, a film containing graphene or graphite can be used for thewiring 511 or the terminal 519.

For example, a film containing graphene formed by reducing a filmcontaining graphene oxide can be used. Specifically, the reduction canbe performed by applying heat, using a reducing agent, or the like.

A conductive high molecule compound can be used for the wiring 511 orthe terminal 519.

<<First Contact 704C and Second Contact 504C>>

The first contact 704C or the second contact 504C can be formed using aconductive material. For example, the materials of the wiring 511 or theterminal 519 can be used.

<<Bonding Layer 505 and Sealant 705>>

An inorganic material, an organic material, a composite material of aninorganic material and an organic material, or the like can be used forthe bonding layer 505 or the sealant 705.

For example, an organic material, such as a resin having thermalfusibility or a curable resin, can be used for the bonding layer 505 orthe sealant 705.

For example, an organic material, such as a reactive curable adhesive, alight curable adhesive, a thermosetting adhesive, and/or an anaerobicadhesive, can be used for the bonding layer 505 or the sealant 705.

Specifically, an adhesive containing an epoxy resin, an acrylic resin, asilicone resin, a phenol resin, a polyimide resin, an imide resin, apolyvinyl chloride (PVC) resin, a polyvinyl butyral (PVB) resin, or anethylene vinyl acetate (EVA) resin, or the like can be used for thebonding layer 505 or the sealant 705.

<<Structures KB1 and KB2>>

The structures KB1 and KB2 can be formed using an organic material, aninorganic material, a composite material of an organic material and aninorganic material, or the like. Accordingly, a predetermined space canbe provided between components between which the structure KB1 or KB2 isprovided.

Specifically, for structures KB1 and KB2, polyester, polyolefin,polyamide, polyimide, polycarbonate, polysiloxane, an acrylic resin, orthe like, or a composite material of a plurality of kinds of resinsselected from these can be used. A photosensitive material can be used.

<<Pixel 702(i,j)>>

The pixel 702(i,j) can include the first display element 750, the seconddisplay element 550, and the functional layer 520.

The pixel 702(i,j) can include the coloring film CF1, the light-blockingfilm BM, the insulating film 771, the alignment film AF1, the alignmentfilm AF2, and the coloring film CF2.

<<First Display Element 750>>

For example, a display element having a function of controllingtransmission or reflection of light can be used as the first displayelement 750. For example, a combined structure of a polarizing plate anda liquid crystal element or a MEMS shutter display element can be used.The use of a reflective display element can reduce power consumption ofa display panel. Specifically, a reflective liquid crystal displayelement can be used as the first display element 750.

Specifically, a liquid crystal element that can be driven by any of thefollowing driving methods can be used: an in-plane switching (IPS) mode,a twisted nematic (TN) mode, a fringe field switching (FFS) mode, anaxially symmetric aligned micro-cell (ASM) mode, an opticallycompensated birefringence (OCB) mode, a ferroelectric liquid crystal(FLC) mode, an antiferroelectric liquid crystal (AFLC) mode, and thelike.

In addition, a liquid crystal element that can be driven by, forexample, a vertical alignment (VA) mode such as a multi-domain verticalalignment (MVA) mode, a patterned vertical alignment (PVA) mode, anelectrically controlled birefringence (ECB) mode, a continuous pinwheelalignment (CPA) mode, or an advanced super view (ASV) mode can be used.

For example, thermotropic liquid crystal, low-molecular liquid crystal,high-molecular liquid crystal, polymer dispersed liquid crystal,ferroelectric liquid crystal, or anti-ferroelectric liquid crystal canbe used. These liquid crystal materials exhibit a cholesteric phase, asmectic phase, a cubic phase, a chiral nematic phase, an isotropicphase, or the like depending on conditions. Alternatively, a liquidcrystal material which exhibits a blue phase can be used.

For example, the liquid crystal element 750 can include the layer 753containing a liquid crystal material, the first conductive film 751, andthe second conductive film 752. The first conductive film 751 and thesecond conductive film 752 are disposed to apply an electric field forcontrolling the alignment of the liquid crystal material.

The first conductive film 751 or the second conductive film 752 can beformed using a conductive material.

For example, the material of the wiring 511 can be used for the firstconductive film 751 or the second conductive film 752.

<<Reflective Film>>

The reflective film can be formed of a material reflecting light whichpasses through the layer 753 containing a liquid crystal material, inwhich case the first display element 750 can be a reflective liquidcrystal element.

Alternatively, a material or the like with an uneven surface can be usedfor the reflective film, in which case incident light is reflected invarious directions to display white.

Note that the first conductive film 751 formed using a materialreflecting visible light can be used as the reflective film.

Other structures may be used as the reflective film without limitationto the first conductive film 751. For example, a reflective filmcontaining a material reflecting visible light may be provided betweenthe layer 753 containing a liquid crystal material and the firstconductive film 751. Alternatively, the first conductive film 751 formedusing a light-transmitting and conductive material may be providedbetween a reflective film containing a material reflecting visible lightand the layer 753 containing a liquid crystal material.

Note that the second conductive film 752 can be formed using theconductive material transmitting visible light.

For example, a conductive oxide or a conductive oxide containing indiumcan be used for the second conductive film 752. Alternatively, a metalfilm thin enough to transmit light can be used as the second conductivefilm 752.

Specifically, indium oxide, indium tin oxide, indium zinc oxide, zincoxide, zinc oxide to which gallium is added, or the like can be used forthe second conductive film 752.

<<Opening 751H>>

The ratio of the total area of the opening 751H in the reflective filmin one pixel to that of a portion of the reflective film other than theopening is preferably more than or equal to 0.052 and less than or equalto 0.6. If the ratio of the total area of the opening 751H is too large,display performed using the first display element 750 is dark. If theratio of the total area of the opening 751H is too small, displayperformed using the second display element 550 is dark.

In the case where the first conductive film 751 is used as thereflective film, the area of one opening 751H is larger than or equal to3 μm² and smaller than or equal to 25 μm². If the area of the opening751H in the first conductive film 751 is too large, electric field isnot uniformly applied to the layer 753 containing a liquid crystalmaterial, which lowers the display performance of the first displayelement 750. If the area of the opening 751H in the first conductivefilm 751 is too small, light emitted from the second display element 550is not efficiently extracted for display.

The opening 751H may have a polygonal shape, a quadrangular shape, anelliptical shape, a circular shape, a cross shape, a stripe shape, aslit-like shape, or a checkered pattern, for example (see FIG. 1B andFIG. 6A). The opening 751H may be close to the next pixel (see FIG. 6B).The opening 751H is provided close to preferably a pixel emitting lightof the same color, in which case an undesired phenomenon in which lightemitted from the second display element 550 enters a coloring film ofthe adjacent pixel, which is called cross talk, can be suppressed.

Note that the opening 751H is preferably not provided in a regionoverlapping with a seam between the coloring films CF1 transmittingdifferent colors, in which case light emitted from the second displayelement 550 is less likely to reach a coloring film of the adjacentpixel. As a result, a display panel with high color reproducibility canbe produced.

<<Second Display Element 550>>

A light-emitting element, for example, can be used as the second displayelement 550. Specifically, an organic electroluminescence element, aninorganic electroluminescence element, a light-emitting diode, or thelike can be used for the second display element 550.

For example, a stack formed to emit white light can be used as the layer553 containing a light-emitting organic material. Specifically, a stackof a layer containing a light-emitting organic material containing afluorescent material that emits blue light, a layer containing amaterial that is other than a fluorescent material and that emits greenlight and/or red light, or a layer containing a material that is otherthan a fluorescent material and that emits yellow light can be used asthe layer 553 containing a light-emitting organic material.

For example, a material used for the wiring 511 can be used for thethird conductive film 551 or the fourth conductive film 552.

For example, a conductive material that transmits visible light can beused for the third conductive film 551.

For example, a conductive material that transmits visible light can beused for the fourth conductive film 552.

Specifically, conductive oxide, indium-containing conductive oxide,indium oxide, indium tin oxide, indium zinc oxide, zinc oxide, zincoxide to which gallium is added, or the like can be used for the thirdconductive film 551.

Alternatively, a metal film that is thin enough to transmit light can beused as the third conductive film 551.

<<Functional Layer 520>>

The functional layer 520 includes the pixel circuit 730(0, the firstcontact 704C, and the second contact 504C. The functional layer 520includes the insulating film 501A, the insulating film 501B, theinsulating film 501C, the insulating film 521A, the insulating film521B, or the insulating film 528.

<<Pixel Circuit 730(i,j)>>

A circuit electrically connected to the scan line G1(i), the scan lineG2(j), the signal line S(j), the wiring ANO, the wiring VCOM1, and thewiring VCOM2 can be used as the pixel circuit 730(i,j) (see FIG. 1C).

Specifically, the pixel circuit 730(i,j) can include the switch SW1, thecapacitor C1, the switch SW2, the capacitor C2, and the transistor M.

The switch SW1 includes a control electrode and a first electrode whichare electrically connected to the scan line G1(i) and the signal line5(j), respectively. Note that the switch SW1 may be a transistor.

The capacitor C1 includes a first electrode and a second electrode whichare electrically connected to a second electrode of the switch SW1 andthe wiring VCOM1, respectively.

Note that the first conductive film 751 and the second conductive film752 of the first display element 750 can be electrically connected tothe second electrode of the switch SW1 and the wiring VCOM1,respectively.

The switch SW2 includes a control electrode and a first electrode whichare electrically connected to the scan line G2(i) and the signal line5(j), respectively. Note that the switch SW2 may be a transistor.

The transistor M includes a gate electrode and a first electrode whichare electrically connected to a second electrode of the switch SW2 andthe wiring ANO, respectively.

The capacitor C2 includes a first electrode and a second electrode whichare electrically connected to the second electrode of the switch SW2 anda second electrode of the transistor M, respectively.

Note that the third conductive film 551 and the fourth conductive film552 of the second display element 550 can be electrically connected tothe second electrode of the transistor M and the wiring VCOM2,respectively.

<<Transistor M>>

The transistor M includes the semiconductor film 508 and the conductivefilm 504 which includes a region overlapping with the semiconductor film508 (see FIG. 2B). The transistor M includes the conductive film 512A,the conductive film 512B, and the insulating film 506 between thesemiconductor film 508 and the conductive film 504.

Note that the conductive film 504 serves as a gate electrode, and theinsulating film 506 serves as a gate insulating film. The conductivefilm 512A has one of a function as a source electrode and a function asa drain electrode, and the conductive film 512B has the other.

Note that the functional layer 520 can include the insulating film 516and the insulating film 518 which cover the transistor M, therebysuppressing impurity diffusion to the transistor M.

As the transistor M, a bottom-gate transistor, a top-gate transistor, orthe like can be used.

For example, a transistor including a semiconductor containing anelement of Group 4 can be used. Specifically, a semiconductor containingsilicon can be used for a semiconductor film. For example, singlecrystal silicon, polysilicon, microcrystalline silicon, amorphoussilicon, or the like can be used for the semiconductor films of thetransistors.

For example, a transistor including an oxide semiconductor can be used.Specifically, an oxide semiconductor containing indium or an oxidesemiconductor containing indium, gallium, and zinc can be used for asemiconductor film.

For example, a transistor having a lower leakage current in an off statethan a transistor that uses amorphous silicon for a semiconductor filmcan be used. Specifically, a transistor that uses an oxide semiconductorfor a semiconductor film can be used.

A pixel circuit in the transistor that uses an oxide semiconductor forthe semiconductor film can hold an image signal for a longer time than apixel circuit in a transistor that uses amorphous silicon for asemiconductor film Specifically, the selection signal can be supplied ata frequency of lower than 30 Hz, preferably lower than 1 Hz, morepreferably less than once per minute while flickering is suppressed.Consequently, eyestrain on a user of the information processing devicecan be reduced, and power consumption for driving can be reduced.

Alternatively, for example, a transistor including a compoundsemiconductor can be used. Specifically, a semiconductor containinggallium arsenide can be used for a semiconductor film.

For example, a transistor including an organic semiconductor can beused. Specifically, an organic semiconductor containing any ofpolyacenes and graphene can be used for the semiconductor film.

<<Switches SW1 and SW2>>

A transistor can serve as the switches SW1 and SW2.

For example, a transistor which can be fabricated in the same process asthe transistor M can be used as the switches SW1 and SW2.

<<Insulating Film 501A>>

The insulating film 501A can be formed using an inorganic oxide film, aninorganic nitride film, an inorganic oxynitride film, or a materialstacking any of these films. Specifically, the insulating film 501A canbe formed using silicon oxide, silicon nitride, silicon oxynitride,aluminum oxide, or a material stacking a plurality of them.

Specifically, a film containing a stacked-layer material of a600-nm-thick silicon oxynitride film and a 200-nm-thick silicon nitridefilm can be used as the insulating film 501A.

Specifically, a film containing a stacked-layer material of a600-nm-thick silicon oxynitride film, a 200-nm-thick silicon nitridefilm, a 200-nm-thick silicon oxynitride film, a 140-nm-thick siliconnitride oxide film, and a 100-nm-thick silicon oxynitride film stackedin this order can be used as the insulating film 501A.

Alternatively, the insulating film 501A can be formed using a materialcontaining resin, such as polyimide.

An insulating film is formed over a substrate for use in manufacturingprocesses and is separated from the substrate to be used as theinsulating film 501A. In that case, the thickness of the insulating film501A can be 5 μm or less, preferably 1.5 μm or less, further preferably1 μm or less.

<<Insulating Film 501B and Insulating Film 501C>>

For example, an insulating inorganic material, an insulating organicmaterial, or an insulating composite material containing an inorganicmaterial and an organic material can be used for the insulating film501B and the insulating film 501C.

Specifically, an inorganic oxide film, an inorganic nitride film, aninorganic oxynitride film, or a material stacking any of these films canbe used for the insulating film 501B and the insulating film 501C. Forexample, a silicon oxide film, a silicon nitride film, an aluminum oxidefilm, a silicon oxynitride film, or a material stacking any of thesefilms can be used for the insulating film 501B and the insulating film501C.

For example, the material which can be used for the insulating film 501Acan be used for the insulating film 501C.

Specifically, for the insulating film 501B and the insulating film 501C,polyester, polyolefin, polyamide, polyimide, polycarbonate,polysiloxane, an acrylic resin, and the like, or a stacked material ofor a composite material of a plurality of kinds of resins selected fromthese can be used. Alternatively, a photosensitive material can be used.

<<Insulating Films 521A, 521B, and 528>>

The materials which can be used for the insulating film 501B or theinsulating film 501C can be used for the insulating film 521A, 521B, or528.

Thus, steps due to components overlapping with the insulating film 521A,for example, can be covered so that a flat surface can be formed. Theinsulating film 521B provided between a plurality of wirings can preventshort circuit of the plurality of wirings. The insulating film 528having an opening which overlaps with the third conductive film 551 canprevent short circuit between the third conductive film 551 and thefourth conductive film which can occur at the edges of the thirdconductive film 551.

<<Coloring Films CF1 and CF2>>

The coloring film CF1 can be formed using a material transmitting lightof a predetermined color, and can thus be used as a color filter or thelike.

For example, the coloring film CF1 can be formed using a materialtransmitting light of blue, green, red, yellow, or white.

The coloring film CF2 can be formed using, for example, the material ofthe coloring film CF1, specifically, a material transmitting lightpassing through the coloring film CF1. In that case, part of lightemitted from the second display element 550 that passes through thecoloring film CF2, the opening 751H, and the coloring film CF1 can beextracted to the outside of the display panel. Note that a materialhaving a function of converting the emitted light to a predeterminedcolor light can be used for the color film CF2. Specifically, quantumdots can be used for the color film CF2. Thus, display with high colorpurity can be achieved.

<<Light-Blocking Film BM>>

A material that prevents light transmission can be used for thelight-blocking film BM, in which case the light-blocking film BM servesas a black matrix, for example.

<<Insulating Film 771>>

The insulating film 771 can be formed of polyimide, epoxy resin, acrylicresin, or the like.

<<Alignment Films AF1 and AF2>>

The alignment films AF1 and AF2 can be formed of a material containingpolyimide or the like, such as a material formed to have a predeterminedalignment by a rubbing process or an optical alignment process.

<<Optical Film 770P>>

For example, a polarizing plate, a retardation plate, a diffusing film,an anti-reflective film, a condensing film, or the like can be used asthe optical film 770P. Alternatively, a polarizing plate containing adichromatic pigment can be used for the optical film 770P.

Alternatively, an antistatic film preventing the attachment of a foreignsubstance, a water repellent film suppressing the attachment of stain, ahard coat film suppressing a scratch in use, or the like can be used forthe optical film 770P.

<<Driver Circuit GD>>

Any of a variety of sequential circuits, such as a shift register, canbe used as the driver circuit GD. For example, the transistor MD, acapacitor, and the like can be used in the driver circuit GD.Specifically, a transistor including a semiconductor film that can beformed at the same step as the transistor M can be used.

As the transistor MD, a transistor different from the transistor M canbe used, such as a transistor including the conductive film 524. Thesemiconductor film 508 is provided between the conductive films 524 and504. The insulating film 516 is provided between the conductive film 524and the semiconductor film 508. The insulating film 506 is providedbetween the semiconductor film 508 and the conductive film 504. Forexample, the conductive film 524 is electrically connected to a wiringsupplying the same potential as that supplied to the conductive film504.

Note that the transistor MD can have the same structure as thetransistor M.

<<Driver Circuit SD>>

For example, an integrated circuit can be used in the driver circuit SD.Specifically, an integrated circuit formed over a silicon substrate canbe used.

For example, a chip on glass (COG) method can be used to mount thedriver circuit SD on a pad provided over the insulating film 501C.Specifically, a conductive material film can be used to mount theintegrated circuit on the pad. Note that the pad is electricallyconnected to the pixel circuit 730(i,j).

<Structure Example 2 of Display Panel>

Another structure of the display panel of one embodiment of the presentinvention will be described with reference to FIGS. 3A and 3B.

FIG. 3A is a cross-sectional view illustrating cross-sectionalstructures of the display panel 700B of one embodiment of the presentinvention taken along the section lines X1-X2, X3-X4, and X5-X6 in FIG.1A. FIG. 3B is a cross-sectional view illustrating the transistor MB orthe transistor MDB in FIG. 3A.

Structures different from those in the display device described inStructure example 1 will be described in detail below, and the abovedescription is referred to for the other similar structures.

Specifically, the display panel 700B in FIGS. 3A and 3B is differentfrom the display panel 700 in FIGS. 2A to 2C in that the coloring filmCF2 is omitted, that the second display element 550B emitting light ofblue, green, red, or the like, that top gate transistors MB and MDB areprovided, that a terminal 519B electrically connected to the wiring 511using a through electrode is provided, and that an insulating film 570Bis provided instead of the substrate 570.

<<Second Display Element 550B>>

In one pixel (also referred to as sub-pixel), the second display element550B that emits light of a color different from that emitted from thesecond display element provided in another sub-pixel is used. Forexample, the second display element 550B that emits blue light is usedin one pixel, and the second display element that emits green light orred light is used in another pixel.

Specifically, an organic EL element including a layer 553B containing alight-emitting organic compound that emits blue light is used in thesecond display element 550B. An organic EL element including a layercontaining a light-emitting organic compound that emits green light orred light is used in another pixel.

Note that an evaporation method, an ink-jet method, or a printing methodusing a shadow mask can be employed to form the layer containing alight-emitting organic compound. In that case, in one pixel, the layercontaining a light-emitting organic compound that emits light of a colordifferent from that emitted from the second display element provided inanother pixel can be used.

Note that the second display element 550B may have a concave shape, andemitted light may be gathered into the opening 751H. Thus, a regionhaving a light-emitting function of the second display element 550B canbe widened to a region not overlapping with the opening 751H. Forexample, the area of the region not overlapping with the opening 751Hcan be 20% or more of the area of a region overlapping with the opening751H. Accordingly, the density of current flowing through the seconddisplay element 550B can be reduced, and for example, heat generationcan be suppressed. Furthermore, reliability can be improved.Furthermore, the area of the opening 751H can be reduced.

<<Transistor MB>>

The transistor MB includes the conductive film 504 having a regionoverlapping with an insulating film 501C and the semiconductor film 508having a region provided between the insulating film 501C and theconductive film 504. Note that the conductive film 504 functions as agate electrode (see FIG. 3B).

The semiconductor film 508 is consisted of a first region 508A, a secondregion 508B, and a third region 508C. The first region 508A and thesecond region 508B do not overlap with the conductive film 504. Thethird region 508C is positioned between the first region 508A and thesecond region 508B and overlaps with the conductive film 504.

The transistor MB includes an insulating film 506 between the thirdregion 508C and the conductive film 504. Note that the insulating film506 functions as a gate insulating film.

The first region 508A and the second region 508B have a lower resistancethan the third region 508C, and function as a source region and a drainregion.

Note that, for example, a method for controlling the resistivity of theoxide semiconductor film to be described later can be used as a methodfor forming the first region 508A and the second region 508B in thesemiconductor film 508. Specifically, plasma treatment using a gascontaining a rare gas can be used. For example, when the conductive film504 is used as a mask, the shape of part of the third region 508C can bethe same as the shape of an end portion of the conductive film 704.

The transistor MB includes the conductive films 512A and 512B which arein contact with the first region 508A and the second region 508B,respectively. The conductive film 512A serves as one of the sourceelectrode and drain electrode, and the conductive film 512B serves asthe other thereof.

The transistor which can be formed in the same process as the transistorMB can be used as the transistor MDB or the switch SW1.

<<Terminal 519B>>

A conductive film formed in the opening in the insulating films 501A,501B, and 501C can be used for the through electrode. Thus, the terminal519B can be provided on the side of the insulating film 501A, 501B, or501C opposite to the side where the pixel circuit is provided. That is,the insulating film 501A, 501B, and 501C can be provided between thepixel circuit and the terminal 519B.

<<Insulating Film 570B>>

As the insulating film 570B, an insulating film having a thickness ofmore than or equal to 50 nm and less than 10 μm, preferably more than orequal to 100 nm and less than 5 μm, can be used, for example.Specifically, such an insulating film may be formed on a substrate foruse in manufacturing processes and be transferred therefrom to adifferent substrate. The thickness of the display panel 700B can thus besmall.

Specifically, a film containing a stacked-layer material of a600-nm-thick silicon oxynitride film and a 200-nm-thick silicon nitridefilm can be used as the insulating film 570B.

Specifically, a film containing a stacked-layer material of a600-nm-thick silicon oxynitride film, a 200-nm-thick silicon nitridefilm, a 200-nm-thick silicon oxynitride film, a 140-nm-thick siliconnitride oxide film, and a 100-nm-thick silicon oxynitride film stackedin this order can be used as the insulating film 570B.

<Structure Example 3 of Display Panel>

Another structure of a display panel of one embodiment of the presentinvention will be described with reference to FIG. 7.

FIG. 7 is a cross-sectional view illustrating cross-sectional structuresof a display panel 700C of one embodiment of the present invention takenalong the section lines X1-X2, X3-X4, and X5-X6 in FIG. 1.

Structures different from those in the display device described inStructure example 1 will be described in detail below, and the abovedescription is referred to for the other similar structures.

Specifically, the display panel in FIG. 7 is different from that inFIGS. 2A to 2C in that the coloring films CF1 and CF2 are omitted, thesecond display element 550B emits light of blue, green, red, or thelike, that a fourth insulating film 501D is provided between theinsulating film 501A and the insulating film 501B, that a secondconductive film 752C instead of the second conductive film 752 isprovided between the insulating film 501A and the fourth insulating film501D, and that the second conductive film 752C has a comb-like shape.

With such a structure, the first conductive film 751 and the secondconductive film 752C can apply a horizontal electric field in thethickness direction of the layer 753 containing a liquid crystalmaterial; thus, the first display element 750 can be driven in an FFSmode.

<<Fourth Insulating Film 501D>>

The fourth insulating film 501D can be formed using any of the materialswhich can be used for the insulating film 501A and the insulating film501B.

<Method for Controlling Resistivity of Oxide Semiconductor Film>

The method for controlling the resistivity of an oxide semiconductorfilm will be described.

An oxide semiconductor film with a certain resistivity can be used forthe semiconductor film 508, the conductive film 524, the first region508A, or the second region 508B.

For example, a method for controlling the concentration of impuritiessuch as hydrogen and water contained in the oxide semiconductor and/orthe oxygen vacancies in the film can be used as the method forcontrolling the resistivity of an oxide semiconductor film.

Specifically, plasma treatment can be used as a method for increasing ordecreasing the concentration of impurities such as hydrogen and waterand/or the oxygen vacancies in the film.

Specifically, plasma treatment using a gas containing one or more kindsselected from a rare gas (He, Ne, Ar, Kr, Xe), hydrogen, boron,phosphorus, and nitrogen can be employed. For example, plasma treatmentin an Ar atmosphere, plasma treatment in a mixed gas atmosphere of Arand hydrogen, plasma treatment in an ammonia atmosphere, plasmatreatment in a mixed gas atmosphere of Ar and ammonia, or plasmatreatment in a nitrogen atmosphere can be employed. Thus, the oxidesemiconductor film can have a high carrier density and a lowresistivity.

Alternatively, hydrogen, boron, phosphorus, or nitrogen is added to theoxide semiconductor film by an ion implantation method, an ion dopingmethod, a plasma immersion ion implantation method, or the like, so thatthe oxide semiconductor film can have a low resistivity.

Alternatively, an insulating film containing hydrogen is formed incontact with the oxide semiconductor film, and the hydrogen is diffusedfrom the insulating film to the oxide semiconductor film, so that theoxide semiconductor film can have a high carrier density and a lowresistivity.

For example, an insulating film with a hydrogen concentration of greaterthan or equal to 1×10²² atoms/cm³ is formed in contact with the oxidesemiconductor film, in that case hydrogen can be effectively supplied tothe oxide semiconductor film. Specifically, a silicon nitride film canbe used as the insulating film formed in contact with the oxidesemiconductor film.

Hydrogen contained in the oxide semiconductor film reacts with oxygenbonded to a metal atom to be water, and an oxygen vacancy is formed in alattice from which oxygen is released (or a portion from which oxygen isreleased). Due to entry of hydrogen into the oxygen vacancy, an electronserving as a carrier is generated in some cases. Furthermore, bonding ofpart of hydrogen to oxygen bonded to a metal atom causes generation ofan electron serving as a carrier in some cases. Thus, the oxidesemiconductor film can have a high carrier density and a lowresistivity.

Specifically, an oxide semiconductor with a hydrogen concentrationmeasured by secondary ion mass spectrometry (SIMS) of greater than orequal to 8×10¹⁹ atoms/cm³, preferably greater than or equal to 1×10²⁰atoms/cm³, more preferably greater than or equal to 5×10²⁰ atoms/cm³ canbe suitably used for the conductive film 524, the first region 508A, orthe second region 508B.

On the other hand, an oxide semiconductor with a high resistivity can beused for a semiconductor film where a channel of a transistor is formed.

For example, an insulating film containing oxygen, in other words, aninsulating film capable of releasing oxygen, is formed in contact withan oxide semiconductor film, and the oxygen is supplied from theinsulating film to the oxide semiconductor film, so that oxygenvacancies in the film or at the interface can be filled. Thus, the oxidesemiconductor film can have a high resistivity.

For example, a silicon oxide film or a silicon oxynitride film can beused as the insulating film capable of releasing oxygen.

The oxide semiconductor film in which oxygen vacancies are filled andthe hydrogen concentration is reduced can be referred to as a highlypurified intrinsic or substantially highly purified intrinsic oxidesemiconductor film. The term “substantially intrinsic” refers to thestate in which an oxide semiconductor film has a carrier density lowerthan 8×10¹¹/cm³, preferably lower than 1×10¹¹/cm³, further preferablylower than 1×10¹⁰/cm³. A highly purified intrinsic or substantiallyhighly purified intrinsic oxide semiconductor film has few carriergeneration sources and thus can have a low carrier density. The highlypurified intrinsic or substantially highly purified intrinsic oxidesemiconductor film has a low density of defect states and accordinglycan have a low density of trap states.

Furthermore, a transistor including the highly purified intrinsic orsubstantially highly purified intrinsic oxide semiconductor film has anextremely low off-state current; even when an element has a channelwidth of 1×10⁶ μm and a channel length L of 10 μm, the off-state currentcan be lower than or equal to the measurement limit of a semiconductorparameter analyzer, that is, lower than or equal to 1×10⁻¹³ A, at avoltage (drain voltage) between a source electrode and a drain electrodeof from 1 V to 10 V.

The transistor in which a channel region is formed in the oxidesemiconductor film that is a highly purified intrinsic or substantiallyhighly purified intrinsic oxide semiconductor film can have a smallchange in electrical characteristics and high reliability.

Specifically, an oxide semiconductor has a hydrogen concentration whichis measured by secondary ion mass spectrometry (SIMS) of lower than orequal to 2×10²⁰ atoms/cm³, preferably lower than or equal to 5×10¹⁹atoms/cm³, more preferably lower than or equal to 1×10¹⁹ atoms/cm³, morepreferably lower than 5×10¹⁸ atoms/cm³, more preferably lower than orequal to 1×10¹⁸ atoms/cm³, more preferably lower than or equal to 5×10¹⁷atoms/cm³, more preferably lower than or equal to 1×10¹⁶ atoms/cm³ canbe favorably used for a semiconductor film where a channel of atransistor is formed.

An oxide semiconductor film that has a higher hydrogen concentrationand/or a larger number of oxygen vacancies and that has a lowerresistivity than the semiconductor film 508 is used as the conductivefilm 524.

The hydrogen concentration in the conductive film 524 is twice or more,preferably ten times or more that in the semiconductor film 508.

The resistivity of the conductive film 524 is greater than or equal to1×10⁻⁸ times and less than 1×10⁻¹ times that of the semiconductor film508.

Specifically, the resistivity of the conductive film 524 is higher thanor equal to 1×10⁻³ Ωcm and lower than 1×10⁴ Ωcm, preferably higher thanor equal to 1×10⁻³ Ωcm and lower than 1×10⁻¹ Ωcm.

This embodiment can be combined with any of the other embodiments inthis specification as appropriate.

Embodiment 2

In this embodiment, the structure of a display panel of one embodimentof the present invention will be described with reference to FIGS. 1A to1C and FIGS. 8A and 8B.

FIGS. 1A and 1C illustrate the structure of a display panel of oneembodiment of the present invention. FIGS. 1A and 1B are top views of adisplay panel 700D of one embodiment of the present invention and thepixel 702(i,j) in FIG. 1A, respectively.

FIGS. 8A to 8C illustrate the structure of the display panel of oneembodiment of the present invention. FIG. 8A is a cross-sectional viewof the display panel 700D taken along the section lines X1-X2, X3-X4,and X5-X6 in FIG. 1A. FIG. 8B is a cross-sectional view of thetransistor M in FIG. 8A. FIG. 8C is a cross-sectional view of thetransistor MD in FIG. 8A.

<Structure Example 1 of Display Panel>

The display panel 700D described in this embodiment includes the pixel702(i,j) and a terminal 519D(1) (see FIG. 1A).

The pixel 702(i,j) includes the insulating film 501B, a first contact591 in an opening provided in the insulating film 501B, the pixelcircuit 730(i,j) electrically connected to the first contact 591, asecond contact 592 electrically connected to the pixel circuit 730(i,j),the first display element 750 electrically connected to the firstcontact 591, and the second display element 550 electrically connectedto the second contact 592 (see FIG. 1C and FIG. 8A).

The insulating film 501B includes a region lying between the firstdisplay element 750 and the second display element 550.

The first display element 750 includes a reflective film which reflectsincident light and has the opening 751H. The first display element 750is configured to control the intensity of the reflected light. Note thatthe first conductive film 751 can be used as the reflective film.

The region of the second display element 550 overlapping with theopening 751H has a function of emitting light toward the opening 751H.

The terminal 519D(1) is electrically connected to the pixel circuit730(i,j) and has a surface at which contact with other component can bemade. The surface at which contact with other component can be madefaces the same direction as a surface of the reflective film whichreflects external light used for performing display.

The pixel circuit 730(i,j) of the display panel 700D includes aswitching element, such as the switch SW1 or SW2 (see FIG. 1C).

The display panel 700D according to one embodiment of the presentinvention includes the pixel 702(i,j) and the terminal 519D(i,j)electrically connected to the pixel. The pixel 702(i,j) includes theinsulating film 501B, the first contact 591 in the opening provided inthe insulating film 501B, the pixel circuit electrically connected tothe first contact 591, the second contact 592 electrically connected tothe pixel circuit 730(i,j), the first display element 750 electricallyconnected to the first contact 591, and the second display element 550electrically connected to the second contact 592. The insulating film501B includes the region lying between the first display element 750 andthe second display element 550. The terminal 519D(i,j) includes thesurface at which contact with other component can be made. The surfaceat which contact with other component can be made faces the samedirection as a surface of the reflective film which reflects externallight used for performing display.

With the structure, the first display element and the second displayelement between which the second insulating film is provided can bedriven using the pixel circuit connected to the terminal, for example.Thus, a novel display panel which is highly convenient or reliable canbe provided.

The pixel circuit 730(i,j) of the display panel 700D also includes atransistor that can be used as a switch and can suppress off-statecurrent more than a transistor including an amorphous silicon as asemiconductor (see FIG. 1C).

Since the pixel circuit 730(i,j) of the display panel 700D includes sucha transistor capable of suppressing off-state current, the frequency ofsupplying a selection signal to the pixel circuit can be reduced whilesuppressing flickers with display. Thus, a novel display panel withreduced power consumption and which is highly convenient or reliable canbe provided.

The first display element 750 of the display panel 700D includes a layer753 containing a liquid crystal material, the first conductive film 751,and the second conductive film 752. The first conductive film 751 andthe second conductive film 752 are provided to control the alignment ofthe liquid crystal material. Electrical connection with the firstconductive film 751 is made at the first contact 591 (see FIG. 8A).

The second display element 550D of the display panel 700 includes athird conductive film 551, a fourth conductive film 552 having a regionoverlapping with the third conductive film 551, and a layer 553containing a light-emitting organic compound between the thirdconductive film 551 and the fourth conductive film 552. The thirdconductive film 551 is electrically connected to the second contact 592and transmits light.

The display panel 700D includes a reflective liquid crystal element andan organic EL element which are respectively used as the first displayelement 750 and the second display element 550.

Owing to the structure, in a bright place, external light and thereflective liquid crystal element are utilized to perform display, whilein a dark place, light emitted from the organic EL element is utilizedto perform display. Thus, a novel display panel highly convenient orreliable can be provided. Thus, a novel display panel capable ofperforming display with high visibility, a novel display panel withreduced power consumption, or a novel display panel highly convenient orreliable can be provided.

The second display element 550 preferably has a function of reflectingexternal light. For example, a material reflecting visible light can beused for the fourth conductive film 552.

The ratio of the total area of one or a plurality of openings includingthe opening 751H in the reflective film to that of a portion of thereflective film other than the openings is more than or equal to 0.052and less than or equal to 0.6. The area of one opening 751H is largerthan or equal to 3 μm² and smaller than or equal to 25 μm². Note that inthe case of using the first conductive film 751 as the reflective film,the ratio of the total area of openings including the opening 751H inthe first conductive film 751 to that of a portion of the firstconductive film 751 other than the openings is more than or equal to0.052 and less than or equal to 0.6 (see FIG. 1B).

When the area of a pixel is assumed to be 1, the area of the reflectivefilm can be more than or equal to 0.5 and less than or equal to 0.95 ofthe area of the pixel. Furthermore, the area of the opening 751H can bemore than or equal to 0.052 and less than or equal to 0.3 of the area ofthe pixel.

Owing to the structure, irregular alignment of the liquid crystalmaterial can be avoided. In addition, in a bright place, external lightand the reflective liquid crystal element are utilized to performdisplay, while in a dark place, light emitted from the organic ELelement is utilized to perform display. Thus, a novel display panelhighly convenient or reliable can be provided.

The reflective film of the display panel 700D includes a region embeddedin the insulating film 501B and a region not covered by the insulatingfilm 501B. For example, in the case where the first conductive film 751is used as the reflective film, a region embedded in the insulating film501B is provided on the side surface of the first conductive film 751and the surface thereof in contact with the first contact 591.

The terminal 519D(1) includes a region embedded in the insulating film501B and a region not covered by the insulating film 501B.

Thus, a step at the edge of the first conductive film can be minimizedto reduce the possibility of alignment defects due to the step. Thus, anovel display panel highly convenient or reliable can be provided.

Note that the display panel 700D can include one or a plurality ofpixels. For example, n pixels 702(i,j) can be arranged in a rowdirection and m pixels 702(i,j) can be arranged in a column directionwhich intersects with the row direction. Note that i is an integergreater than or equal to 1 and less than or equal to m, j is an integergreater than or equal to 1 and less than or equal to n, and each of mand n is an integer greater than or equal to 1.

In addition, the display panel 700D can include scan lines G1(i) andG2(i) electrically connected to pixels 702(i,j) to 702(i,n) arranged inthe row direction (see FIG. 1C).

In addition, the display panel 700D can include a signal line S(j)electrically connected to pixels 702(1,j) to 702(m,j) arranged in thecolumn direction.

In addition, the pixel 702(i,j) of the display panel 700 includes acoloring film CF1 having a region overlapping with the first displayelement 750, a light blocking film BM having an opening in a regionoverlapping with the first display element 750, and an insulating film771 between the coloring film CF1 or the blocking film BM and the layer753 containing a liquid crystal material (see FIG. 8A). Owing to theinsulating film 771, unevenness due to the thickness of the coloringfilm CF1 can be avoided. Alternatively, impurities can be prevented frombeing diffused from the light blocking film BM, the coloring film CF1,or the like to the layer 753 containing a liquid crystal material

The display panel 700D includes an alignment film AF2 between thesubstrate 770 and the layer 753 containing a liquid crystal material andan alignment film AF1 between the layer 753 containing a liquid crystalmaterial and the insulating film 501B.

In the display panel 700D, the layer 753 containing a liquid crystalmaterial is surrounded by the substrate 770, the insulating film 501B,and a sealant 705. The sealant 705 has a function of bonding thesubstrate 770 and the insulating film 501B.

The display panel 700D includes a structure KB1 for the space betweenthe substrate 770 and the insulating film 501B.

The display panel 700D includes an optical film 770P having a regionoverlapping with the pixel 702(i,j). In the display panel 700D, thesubstrate 770 is provided between the optical film 770P and the layer753 containing a liquid crystal material.

The display panel 700D includes the functional layer 520D. Thefunctional layer 520D includes the insulating film 501B, the insulatingfilm 501C, the insulating film 521A, the insulating film 521B, and theinsulating film 528.

The insulating film 501B and the insulating film 501C each have anopening where the first contact 591 is provided and an opening where thethird contact 593 is provided. Although the insulating film 501C isstacked over the insulating film 501B in this embodiment, the insulatingfilm 501C may be omitted.

The insulating film 521B has a region overlapping with the insulatingfilm 501B.

The insulating film 521A lies between the insulating film 501B and theinsulating film 521B.

The insulating film 521A has an opening where the second contact 592 isprovided.

The insulating film 528 has an opening where the second display element550 is provided.

In the display panel 700D, a coloring film CF2 lies between the seconddisplay element 550 and the opening 751H in the reflective film.

The display panel 700D includes a substrate 570 having a regionoverlapping with the functional layer 520D, and a bonding layer 505bonding the functional layer 520D and the substrate 570.

In the display panel 700D, the second display element 550 lies betweenthe functional layer 520D and the substrate 570.

The display panel 700D includes a structure KB2 between the functionallayer 520D and the substrate 570 to provide a space therebetween.

The display panel 700D includes a driver circuit GD. The driver circuitGD includes the transistor MD, for example (see FIG. 1A and FIG. 8A).The driver circuit GD has a function of supplying a selection signal tothe scan line G1(i) or the scan line G2(i), for example.

The display panel 700D includes a wiring 511 and a terminal 519D(1)which are electrically connected to the pixel circuit 730(i,j). Thedisplay panel 700D can include a wiring ANO, a wiring VCOM1, and awiring VCOM2 (see FIG. 1C and FIG. 8A).

Note that a flexible printed circuit board FPC1 can be electricallyconnected to the terminal 519D(1) using a conductive material film ACF1.For example, the display panel 700D can be electrically connected to adriver circuit SD using the conductive material film ACF1.

The display panel 700D can include the terminal 519D(2). The terminal519D(2) is electrically connected to a terminal which can be formed inthe same process for forming the pixel circuit 730(i,j) or the terminal519D(1). One surface of the terminal 519D(2) is contact with othercomponent and faces the same direction as a surface of the reflectivefilm which reflects external light used for performing display. Notethat the terminal 519D(2) can be electrically connected to the secondconductive film 752 using the conductive member CP, for example.

Note that the driver circuit SD supplies an image signal in accordancewith image information.

Components of the display panel 700D will be described below. Note thatthe components cannot be clearly distinguished and one unit serves asanother unit or include part of another unit in some cases.

For example, in the case where a conductive film reflecting visiblelight is used as the first conductive film 751, the first conductivefilm 751 can be used as a reflective film: the first conductive film 751serves as the reflective film, and the reflective film serves as thefirst conductive film 751.

<Structure>

The display panel 700D includes the substrate 570, the substrate 770,the wiring 511, and the terminals 519D(1) and 519D(2) (see FIG. 8A).

The display panel 700D includes the sealant 705, the bonding layer 505,the structure KB1, and the structure KB2.

The display panel 700D includes the pixel 702(i,j), the first displayelement 750, and the second display element 550.

The display panel 700D includes the first conductive film 751, thesecond conductive film 752, the layer 753 containing a liquid crystalmaterial, the opening 751H, and the reflective film.

The display panel 700D includes the third conductive film 551, thefourth conductive film 552, and the layer 553 containing alight-emitting organic compound.

The display panel 700D includes the functional layer 520D, the pixelcircuit 730(1/), the first contact 591, the second contact 592, or thethird contact 593 (see FIG. 8A and FIG. 1C).

The display panel 700D includes the switching element SW1, the switchingelement SW2, the transistor M, the transistor MD, the insulating film501B, the insulating film 501C, the insulating film 521A, the insulatingfilm 521B, and the insulating film 528.

The display panel 700D includes the coloring film CF1, the coloring filmCF2, the light-blocking film BM, the insulating film 771, the alignmentfilm AF1, the alignment film AF2, and the optical film 770P.

The display panel 700D includes the driver circuit GD and the drivercircuit SD.

<<Substrate 570>>

The substrate 570 can be formed using a material having heat resistancehigh enough to withstand heat treatment in the manufacturing process.For example, a material similar to the material which can be used forthe substrate 570 and is described in Embodiment 1 can be used.

<<Substrate 770>>

A light-transmitting material can be used for the substrate 770. Forexample, a material that can be used for the substrate 570 can be usedfor the substrate 770.

<<Wiring 511, Terminal 519D(1), and Terminal 519D(2)>>

A conductive material can be used for the wiring 511, the terminal519D(1), or the terminal 519D(2). For example, a material similar to thematerial which can be used for the wiring 511 or 519 in Embodiment 1 canbe used.

<<First Contact 591, Second Contact 592, and Third Contact 593>>

A conductive material can be used for the first contact 592 or thesecond contact 592. For example, a material similar to the materialwhich can be used for the wiring 511 or the terminal 519D(1) or 519D(2)can be used.

<<Bonding Layer 505 and Sealant 705>>

An inorganic material, an organic material, a composite material of aninorganic material and an organic material, or the like can be used forthe bonding layer 505 or the sealant 705. For example, a materialsimilar to the material of the bonding layer 505 or the sealant 705described in Embodiment 1 can be used.

<<Structures KB1 and KB2>>

The structures KB1 and KB2 can be formed using an organic material, aninorganic material, a composite material of an organic material and aninorganic material, or the like. Accordingly, a predetermined space canbe provided between components between which the structure KB1 or KB2 isprovided. For example, a material similar to the material which can beused for the structure KB1 or KB2 and is described in Embodiment 1 canbe used.

<<Pixel 702(i,j)>>

The pixel 702(i,j) can include the first display element 750, the seconddisplay element 550, and the functional layer 520D.

The pixel 702(i,j) can include the coloring film CF1, the light-blockingfilm BM, the insulating film 771, the alignment film AF1, the alignmentfilm AF2, and the coloring film CF2.

<<First Display Element 750>>

For example, a display element having a function of controllingtransmission or reflection of light can be used as the first displayelement 750. For example, a combined structure of a polarizing plate anda liquid crystal element or a MEMS shutter display element can be used.The use of a reflective display element can reduce power consumption ofa display panel. Specifically, a reflective liquid crystal displayelement can be used as the first display element 750. For example, amaterial similar to the material which can be used for the first displayelement 750 and is described in Embodiment 1 can be used.

<<Reflective Film>>

The reflective film can be formed of a material reflecting light whichpasses through the layer 753 containing a liquid crystal material, inwhich case the first display element 750 can be a reflective liquidcrystal element. For example, a material similar to the material whichcan be used for the reflective film and is described in Embodiment 1 canbe used.

<<Opening 751H>>

For example, the opening described in Embodiment 1 can be used as theopening.

<<Second Display Element 550>>

A light-emitting element, for example, can be used as the second displayelement 550. Specifically, an organic electroluminescence element, aninorganic electroluminescence element, a light-emitting diode, or thelike can be used for the second display element 550.

For example, a stack formed to emit white light can be used as the layer553 containing a light-emitting organic material. Specifically, a stackof a layer containing a light-emitting organic material containing afluorescent material that emits blue light, a layer containing amaterial that is other than a fluorescent material and that emits greenlight and/or red light, or a layer containing a material that is otherthan a fluorescent material and that emits yellow light can be used asthe layer 553 containing a light-emitting organic material.

For example, a material used for the wiring 511 can be used for thethird conductive film 551 or the fourth conductive film 552.

For example, a conductive material that transmits visible light can beused for the third conductive film 551.

For example, a conductive material that transmits visible light can beused for the fourth conductive film 552.

Specifically, conductive oxide, indium-containing conductive oxide,indium oxide, indium tin oxide, indium zinc oxide, zinc oxide, zincoxide to which gallium is added, or the like can be used for the thirdconductive film 551.

Alternatively, a metal film that is thin enough to transmit light can beused as the third conductive film 551.

<<Functional Layer 520D>>

The functional layer 520D includes the pixel circuit 730(0, the firstcontact 591, the second contact 592, and the third contact 593. Thefunctional layer 520D includes the insulating film 501A, the insulatingfilm 501B, the insulating film 501C, the insulating film 521A, theinsulating film 521B, and the insulating film 528.

<<Pixel Circuit 730(i,j)>>

For example, a structure similar to the structure which can be used forthe pixel circuit 730(i,j) and is described in Embodiment 1 can be used.

<<Transistor M>>

The transistor M includes the semiconductor film 508 and the conductivefilm 504 which includes a region overlapping with the semiconductor film508 (see FIG. 8B). The transistor M includes the conductive film 512A,the conductive film 512B, and the insulating film 506 between thesemiconductor film 508 and the conductive film 504. For example, astructure similar to the structure which can be used for the transistorM and is described in Embodiment 1 can be used.

<<Switches SW1 and SW2>>

A transistor can serve as the switch SW1 or SW2.

For example, a transistor which can be fabricated in the same process asthe transistor M can be used as the switch SW1 or SW2.

<<Insulating Film 501B and Insulating Film 501C>>

Although the insulating film 501C is stacked over the insulating film501B in this embodiment, the insulating film 501C may be omitted. Forexample, a material similar to the material which can be used for theinsulating film 501B or the insulating film 501C and is described inEmbodiment 1 can be used.

<<Insulating Films 521A, 521B, and 528>>

For example, a material similar to the material which can be used forthe insulating film 521A, 521B, or 528 and is described in Embodiment 1can be used.

<<Coloring Film CF1 and CF2>>

For example, a material similar to the material which can be used forthe coloring film CF1 or CF2 and is described in Embodiment 1 can beused.

<<Light-Blocking Film BM>>

A material that prevents light transmission can be used for thelight-blocking film BM, in which case the light-blocking film BM servesas a black matrix, for example.

<<Insulating Film 771>>

The insulating film 771 can be formed of polyimide, epoxy resin, acrylicresin, or the like.

<<Alignment Films AF1 and AF2>>

The alignment films AF1 and AF2 can be formed of a material containingpolyimide or the like, such as a material formed to have a predeterminedalignment by a rubbing process or an optical alignment process.

<<Optical Film 770P>>

For example, a material similar to the material which can be used forthe optical film 770P and is described in Embodiment 1 can be used.

<<Driver Circuit GD>>

For example, a structure similar to the structure which can be used forthe driver circuit GD and is described in Embodiment 1 can be used.

<<Driver Circuit SD>>

For example, an integrated circuit can be used in the driver circuit SD.Specifically, an integrated circuit formed over a silicon substrate canbe used.

For example, a chip on glass (COG) method can be used to mount thedriver circuit SD on a pad provided over the insulating film 501C.Specifically, a conductive material film can be used to mount theintegrated circuit on the pad. Note that the pad is electricallyconnected to the pixel circuit 730(i,j).

<Structure Example 2 of Display Panel>

Another structure of a display panel of one embodiment of the presentinvention will be described with reference to FIGS. 9A to 9D.

FIGS. 9A to 9D illustrate structures of a pixel circuit which can beused for the display panel of one embodiment of the present invention.The pixel circuit shown in FIGS. 9A to 9D can be used instead of thepixel circuit 730(i,j) in FIG. 1C.

Note that the pixel circuit 730(i,j) in FIG. 9A is different from thepixel circuit 730(i,j) in FIG. 1C in that it is electrically connectedto signal lines S1(j) and S2(j).

The pixel circuit 730(i,j) shown in FIG. 9B is different from the pixelcircuit 730(i,j) shown in FIG. 1C in that it is electrically connectedto the signal lines S1(j) and S2(j) and that the control electrodes ofthe switches SW1 and SW2 are electrically connected to the scan lineG1(i).

The pixel circuit 730(i,j) shown in FIG. 9C is different from the pixelcircuit 730(i,j) shown in FIG. 1C in that the second electrode of thecapacitor C1 is electrically connected to a wiring CS. Note that awiring other than the wiring VCOM1 can be used as the wiring CS.

The pixel circuit 730(i,j) shown in FIG. 9D is different from the pixelcircuit 730(i,j) shown in FIG. 9A in that the second electrode of thecapacitor C2 is electrically connected to the wiring ANO and that thesecond electrode of the transistor M is electrically connected to thewiring ANO. Note that for example, the transistor M can have a structuresimilar to the transistor MD including the conductive film 524.

<Structure Example 3 of Display Panel>

Another structure of the display panel of one embodiment of the presentinvention will be described with reference to FIG. 10.

FIG. 10 illustrates the structure of the display panel of one embodimentof the present invention. FIG. 10 is a cross-sectional view of a displaypanel 700E, which is one embodiment of the present invention, takenalong the section lines X1-X2, X3-X4, and X5-X6 in FIG. 1A.

Note that the display panel 700E shown in FIG. 10 is different from thedisplay panel 700D shown in FIG. 8A in that the first conductive film751 and the second conductive film 752 include a region embedded in theinsulating film 501B and a region exposed from the insulating film 501Band that the second contact 592 and the third conductive film 551contain the same conductive material.

Specifically, the first display element 750 of the display panel 700Eincludes a liquid crystal display element driven in an IPS mode or thelike.

<Structure Example 4 of Display Panel>

Another structure of the display panel of one embodiment of the presentinvention will be described with reference to FIG. 11.

FIG. 11 illustrates a structure of the display panel of one embodimentof the present invention. FIG. 11 is a cross-sectional view of thedisplay panel 700E, which is one embodiment of the present invention,taken along the section lines X1-X2, X3-X4, and X5-X6 in FIG. 1A.

Note that the display panel 700F in FIG. 11 is different from thedisplay panel 700D in FIG. 8A in that a layer 753T containing electronicink is provided instead of the layer 753 containing a liquid crystalmaterial, that a first transparent conductive film 751T is providedinstead of the first conductive film 751 having the opening 751H, andthat a transparent structure KB3 lies in a region overlapping with thesecond display element 550.

Specifically, the layer 753T containing electronic ink of the displaypanel 700F contains rewritable electronic ink, such as electrophoreticink. By electrical control of the electronic ink, rewriting and erasingcan be performed.

This embodiment can be combined with any of the other embodiments inthis specification as appropriate.

Embodiment 3

In this embodiment, a method for manufacturing a display panel of oneembodiment of the present invention will be described with reference toFIGS. 12 to 19.

FIG. 12 is a flow chart illustrating a method for manufacturing adisplay panel 700D of one embodiment of the present invention. FIGS. 13to 19 are cross-sectional views of the display panel 700D in themanufacturing steps taken along the section lines X1-X2, X3-X4, andX5-X6 of FIG. 1A.

<Method for Manufacturing Display Panel>

The method for manufacturing the display panel 700D described in thisembodiment is composed of the following 11 steps.

<Step 1>

In a step 1, the insulating film 501A is formed over a substrate for usein manufacturing processes (see U1 in FIG. 12). For example, theinsulating film 501A is formed so that a separation film 510W isprovided between the insulating film 501A and a substrate 510.

The substrate for use in manufacturing processes can include, forexample, the substrate 510 and the separation film 510W having a regionoverlapping with the substrate 510.

The substrate 510 can be formed using a material having heat resistancehigh enough to withstand heat treatment in the manufacturing process.

For example, a large-sized glass substrate having any of the followingsizes can be used: the 6th generation (1500 mm×1850 mm), the 7thgeneration (1870 mm×2200 mm), the 8th generation (2200 mm×2400 mm), the9th generation (2400 mm×2800 mm), and the 10th generation (2950 mm×3400mm). Thus, a large-sized LCD can be used as the substrate 510, and alarge-sized display device can be manufactured.

For the substrate 510, an organic material, an inorganic material, acomposite material of an organic material and an inorganic material, orthe like can be used. For example, an inorganic material such as glass,ceramic, or metal can be used for the substrate 510.

Specifically, non-alkali glass, soda-lime glass, potash glass, crystalglass quartz, sapphire, or the like can be used for the substrate 510.Specifically, an inorganic oxide, an inorganic nitride, an inorganicoxynitride, or the like can be used for the substrate 510. For example,a silicon oxide film, a silicon nitride film, a silicon oxynitride film,or an aluminum oxide film can be used for the substrate 510. Stainlesssteel, aluminum, or the like can be used for the substrate 510.

For example, an organic material such as a resin, a resin film, orplastic can be used for the substrate 510. Specifically, a resin film orresin plate of polyester, polyolefin, polyamide, polyimide,polycarbonate, an acrylic resin, or the like can be used for thesubstrate 510.

For example, a composite material such as a resin film to which a metalplate, a thin glass plate, or a film of an inorganic material isattached can be used for the substrate 510. For example, a compositematerial formed by dispersing a fibrous or particulate metal, glass,inorganic material, or the like into a resin film can be used as thesubstrate 510. For example, a composite material formed by dispersing afibrous or particulate resin, organic material, or the like into aninorganic material can be used as the substrate 510.

A single-layer material or a stacked-layer material in which a pluralityof layers are stacked can be used for the substrate 510. For example, astacked-layer material in which a base, an insulating film that preventsdiffusion of impurities contained in the base, and the like are stackedcan be used for the substrate 510.

For example, the separation film 510W can be formed using a materialthat allows the insulating film 501A to be separated from the substrate510 in the step 9.

Note that the separation film 510W can remain on the substrate 510 sideafter the insulating film 501A is separated from the substrate 510.Alternatively, the separation film 510W can be separated together withthe insulating film 501A from the substrate 510.

Specifically, the separation film 510W can remain on the substrate 510side after the insulating film 501A can be separated from the substrate510 in the case where the substrate 510, the separation film 501W, andthe insulating film 501A are formed using a non-alkali glass substrate,a film containing tungsten or the like, and a film containing inorganicoxide or inorganic oxynitride, respectively.

The separation film 510W can be separated together with the insulatingfilm 501A from the substrate 510 when the substrate 510, the separationfilm 510W, and the insulating film 501A are formed using a non-alkaliglass substrate, a film containing polyimide, and a film containingvarious materials, respectively.

For example, the insulating film 501A is formed on the separation film510W by a chemical vapor deposition method, a sputtering method, acoating method, or the like. Then, unnecessary portions are removed by aphotolithography process, or the like so that the insulating film 501Ais completed.

Note that it is preferable that the insulating film 501A be larger thanthe separation film 510W so that the peripheral portion of theinsulating film 501A is in contact with the substrate 510, in which caseoccurrence of unintended separation of the insulating film 501A from thesubstrate for use in manufacturing processes can be reduced.

Specifically, a 0.7-mm-thick glass plate is used as the substrate 510,and a stacked-layer material of a 200-nm-thick silicon oxynitride filmand a 30-nm-thick tungsten film stacked in this order from the substrate510 side is used for the separation film 510W. In addition, a filmincluding a stacked-layer material in which a 600-nm-thick siliconoxynitride film and a 200-nm-thick silicon nitride film are stacked inthis order from the separation film 510W side can be used as theinsulating film 501A. Note that a silicon oxynitride film refers to afilm that includes more oxygen than nitrogen, and a silicon nitrideoxide film refers to a film that includes more nitrogen than oxygen.

Specifically, instead of the insulating film 501A, a film including astacked-layer material of a 600-nm-thick silicon oxynitride film, a200-nm-thick silicon nitride film, a 200-nm-thick silicon oxynitridefilm, a 140-nm-thick silicon nitride oxide film, and a 100-nm-thicksilicon oxynitride film stacked in this order from the separation film510W side can be used.

<<Step 2>>

In a step 2, a reflective film and terminals are formed (see U2 in FIG.12). Note that the first conductive film 751 serves as the reflectivefilm in an example of this embodiment.

The reflective film includes the opening 751H. The terminals include theterminals 519D(1) and 519D(2).

A film containing a conductive material is formed on the insulating film501A by a chemical vapor deposition method, a sputtering method, acoating method, or the like. Then, unnecessary portions are removed by aphotolithography process, so that the first conductive film 751 used asthe reflective film and the terminals 519D(1) and 519D(2) are completed.

<<Step 3>>

In a step 3, the insulating film 501B covering the reflective film andthe terminal is formed (see U3 in FIG. 12). Note that the insulatingfilm 501C having a region overlapping with the insulating film 501B maybe formed successively after the insulating film 501B is formed.

The insulating film 501B and the insulating film 501C have openings.

A film suppressing impurity diffusion is formed to cover the reflectivefilm and the terminal by a chemical vapor deposition method, asputtering method, a coating method, or the like.

Then, an opening reaching the first conductive film 751 and an openingreaching the terminal 519D(1) are formed by a photolithography processor the like, so that the insulating film 501B and the insulating film501C are completed.

<<Step 4>>

In a step 4, the first contact 591 and the third contact 593 are formed(see U4 in FIG. 12 and FIG. 13). The reflective film is electricallyconnected to the first contact 591. The terminal 519D(1) is electricallyconnected to the third contact 593. Note that the conductive film 504serving as a gate electrode of the transistor M, the transistor MD, orthe transistor which can be used as the switch SW1 may be formedtogether with the first contact 591 and the terminal 519D.

A film containing a conductive material is formed to be in contact withthe insulating film 501C, the opening reaching the first conductive film751, and the opening reaching the terminal 519D(1) by a chemical vapordeposition method, a sputtering method, a coating method, or the like.

Then, unnecessary portions are removed by a photolithography process orthe like, so that the first contact 591, the third contact 593, and theconductive film 504 are completed.

<<Step 5>>

In a step 5, a pixel circuit electrically connected to the first contact591 and the third contact 593 is formed (see U5 in FIG. 12).

A film containing a conductive material, a film containing an insulatingmaterial, a film containing a semiconductor material, and the like areformed by a chemical vapor deposition method, a sputtering method, orthe like. Then, unnecessary portions of the films are removed by aphotolithography method or the like. With combination of a depositionmethod and a photolithography method or the like, the pixel circuitincluding the transistor M, the transistor MD, and the transistor or thelike serving as the switch SW1 is completed.

Next, the insulating films 516 and 518 protecting elements, such astransistors, of the pixel circuit are formed. Furthermore, theconductive film 524 serving as a second gate electrode is formed betweenthe insulating films 516 and 518.

Then, the coloring film CF2 is formed.

Then, the insulating film 521A is formed. An opening reaching the pixelcircuit is formed in the insulating films 516, 518, and 521A.

<<Step 6>>

In a step 6, the second contact 592 electrically connected to the pixelcircuit is formed (see U6 in FIG. 12 and FIG. 14). Note that a wiringmay be formed together with the second contact 592.

For example, a film containing a conductive material is formed by achemical vapor deposition method, a sputtering method, a coating method,or the like.

Then, unnecessary portions of the films are removed by aphotolithography method or the like to form the second contact 592.

<<Step 7>>

In a step 7, the second display element 550 electrically connected tothe second contact 592 is formed (see U7 in FIG. 12 and FIG. 15).

For example, the insulating film 521B is formed between the secondcontact 592 and the second display element 550.

Next, to form the third conductive film 551 electrically connected tothe second contact 592, a film containing a conductive material isformed by a chemical vapor deposition method, a sputtering method, orthe like. Then, unnecessary portions are removed by a photolithographymethod, so that the third conductive film 551 is finished.

Next, the insulating film 528 having an opening in a region overlappingwith the third conductive film 551 is formed. Note that the ends of thethird conductive film 551 are covered by the insulating film 528. Forexample, a photosensitive polymer film is formed by a coating method orthe like, and its unnecessary portions are removed by a photolithographymethod or the like, so that the insulating film 528 is finished.

Then, the structure KB2 in contact with the insulating film 528 isformed by a method similar to that of the insulating film 528, forexample.

Then, the layer 553 containing a light-emitting organic compound isformed to cover the third conductive film 551 exposed in the opening ofthe insulating film 528. An evaporation method, a printing method, anink-jet method, or the like using a shadow mask can be used.

Then, the fourth conductive film 552 is formed such that the layer 553containing a light-emitting organic compound is provided between thethird conductive film 551 and the fourth conductive film 552.Specifically, an evaporation method, a sputtering method, or the likeusing a shadow mask can be used. Note that the fourth conductive film552 is electrically connected to the wiring 511.

<<Step 8>>

In a step 8, the substrate 570 is stacked (see U8 in FIG. 12 and FIG.16).

A fluid resin or the like is applied to form the bonding layer 505.Specifically, a coating method, a printing method, an ink-jet method, orthe like can be used. Alternatively, a sheet-like fluid resin or thelike is bonded to form the bonding layer 505.

Then, the functional layer 520D and the substrate 570 are bonded usingthe bonding layer 505.

<<Step 9>>

In a step 9, the substrate 510 for use in manufacturing processes isseparated (see U9 in FIG. 12 and FIG. 17).

For example, part of the separation film 510W can be removed from theinsulating film 501A by sticking a sharp tip into the separation film510W from the substrate 510 for use in manufacturing processes, or by amethod using a laser or the like (e.g., a laser ablation method),thereby forming a separation starting point.

Then, the substrate 510 for use in manufacturing processes is graduallyseparated from the separation starting point.

Note that the separation may be performed while the vicinity of theinterface between the separation film 510W and the insulating film 501Ais irradiated with ions to remove static electricity. Specifically, theions may be generated by an ionizer. Alternatively, a liquid may beejected and sprayed by a nozzle to the interface between the separationfilm 510W and the insulating film 501A. For example, as the liquid to beinjected or the liquid to be sprayed, water, a polar solvent, a liquidwhich dissolves the separation film 510W, or the like can be used. Byinjecting such a liquid, influence of static electricity and the likeaccompanying the separation can be reduced.

Particularly in the case where a film containing tungsten oxide is usedfor the separation film 510W, the substrate 510 is separated while awater-containing liquid is injected or sprayed, which leads to areduction in stress with separation.

<<Step 10>>

In a step 10, the insulating film 501A is removed to expose thereflective film and the terminal (see U10 in FIG. 12 and FIG. 18).

The insulating film 501A can be removed by etching, chemical mechanicalpolishing, or the like, such as wet etching or dry etching.

<<Step 11>>

In a step 11, the first display element is formed (see U11 in FIG. 12and FIG. 19).

A counter substrate is prepared. Specifically, the substrate 770including the light blocking film BM, the coloring film CF1, theinsulating film 771, the second conductive film 752, the structure KB1,and the alignment film AF2 is prepared as the counter substrate.

Then, the alignment film AF1 including a region overlapping with theinsulating film 501B and the first conductive film 751 is formed using aprinting method, a rubbing method, and the like.

The sealant 705 is formed. Specifically, a fluid resin is applied toform a frame-like shape using a dispensing method, a printing method, orthe like. Note that a material containing the conductive member CP isapplied to a region of the sealant 705 overlapping with the terminal519D(2).

Then, a liquid crystal material is dropped in the region surrounded bythe sealant 705 using a dispensing method.

Then, the substrate 770 is bonded to the insulating film 501B using thesealant 705. Note that the structure KB1 is provided between theinsulating film 501B and the substrate 770 to electrically connect theterminal 519D(2) and the second conductive film 752 using the conductivemember CP.

The manufacturing method of the display panel 700D in this embodimentincludes the step for separating the substrate 510 for use inmanufacturing processes and the step for removing the insulating film501A to expose the reflective film and the terminal. Accordingly, a stepat the edge of the reflective film can be minimized to reduce thepossibility of alignment defects due to the step. In addition, thesurface of the terminal at which contact with other components is madecan be exposed. A manufacturing method of a novel display panel that ishighly convenient or reliable can be thus provided.

This embodiment can be combined with any of the other embodiments inthis specification as appropriate.

Embodiment 4

In this embodiment, the structure of a transistor which can be used forthe display panel of one embodiment of the present invention will bedescribed with reference to FIGS. 20A to 20C.

<Structural Example of Semiconductor Device>

FIG. 20A is a top view of the transistor 100. FIG. 20B is across-sectional view taken along the section line X1-X2 in FIG. 20A, andFIG. 20C is a cross-sectional view taken along the section line Y1-Y2 inFIG. 20A. Note that in FIG. 20A, some components of the transistor 100(e.g., an insulating film serving as a gate insulating film) are notillustrated to avoid complexity. In some cases, the direction of thesection line Y1-Y2 is referred to as a channel length direction and thedirection of the section line X1-X2 is referred to as a channel widthdirection. As in FIG. 20A, some components might not be illustrated insome top views of transistors described below.

Note that the transistor 100 can be used in the display panel describedin Embodiment 1 or 2.

For example, when the transistor 100 is used as the transistor M, asubstrate 102, a conductive film 104, a stacked film of an insulatingfilm 106 and an insulating film 107, an oxide semiconductor film 108, aconductive film 112 a, a conductive film 112 b, a stacked film of aninsulating film 114 and an insulating film 116, and an insulating film118 can be referred to as the insulating film 501C, the conductive film504, the insulating film 506, the semiconductor film 508, the conductivefilm 512A, the conductive film 512B, an insulating film 516, and theinsulating film 518, respectively.

The transistor 100 includes a conductive film 104 functioning as a gateelectrode over a substrate 102, an insulating film 106 over thesubstrate 102 and the conductive film 104, an insulating film 107 overthe insulating film 106, an oxide semiconductor film 108 over theinsulating film 107, and conductive films 112 a and 112 b functioning assource and drain electrodes electrically connected to the oxidesemiconductor film 108. Over the transistor 100, specifically, over theconductive films 112 a and 112 b and the oxide semiconductor film 108,insulating films 114, 116, and 118 are provided. The insulating films114, 116, and 118 function as protective insulating films for thetransistor 100.

The oxide semiconductor film 108 includes a first oxide semiconductorfilm 108 a on the conductive film 104 side and a second oxidesemiconductor film 108 b over the first oxide semiconductor film 108 a.Furthermore, the insulating films 106 and 107 function as gateinsulating films of the transistor 100.

An In-M oxide (M is Ti, Ga, Sn, Y, Zr, La, Ce, Nd, or Hf) or an In-M-Znoxide can be used for the oxide semiconductor film 108. It isparticularly preferable to use an In-M-Zn oxide for the semiconductorfilm 108.

The first oxide semiconductor film 108 a includes a first region inwhich the atomic proportion of In is larger than the atomic proportionof M. The second oxide semiconductor film 108 b includes a second regionin which the atomic proportion of In is smaller than that in the firstoxide semiconductor film 108 a. The second region include a portionthinner than the first region.

The first oxide semiconductor film 108 a including the first region inwhich the atomic proportion of In is larger than that of M can increasethe field-effect mobility (also simply referred to as mobility or μFE)of the transistor 100. Specifically, the field-effect mobility of thetransistor 100 can exceed 10 cm²/Vs.

For example, the use of the transistor with high field-effect mobilityfor a gate driver that generates a gate signal (specifically, ademultiplexer connected to an output terminal of a shift registerincluded in a gate driver) allows a semiconductor device or a displaydevice to have a narrow frame.

On the other hand, the first oxide semiconductor film 108 a includingthe first region in which the atomic proportion of In is larger thanthat of M makes it easier to change electrical characteristics of thetransistor 100 in light irradiation. However, in the semiconductordevice of one embodiment of the present invention, the second oxidesemiconductor film 108 b is formed over the first oxide semiconductorfilm 108 a. In addition, the thickness of a portion including a channelregion and the vicinity of the channel region in the second oxidesemiconductor film 108 b is smaller than the thickness of the firstoxide semiconductor film 108 a.

Furthermore, the second oxide semiconductor film 108 b includes thesecond region in which the atomic proportion of In is smaller than thefirst oxide semiconductor film 108 a and thus has larger Eg than that ofthe first oxide semiconductor film 108 a. For this reason, the oxidesemiconductor film 108 which is a layered structure of the first oxidesemiconductor film 108 a and the second oxide semiconductor film 108 bhas high resistance to a negative bias stress test with lightirradiation.

The amount of light absorbed by the oxide semiconductor film 108 can bereduced during light irradiation. As a result, the change in electricalcharacteristics of the transistor 100 due to light irradiation can bereduced. In the semiconductor device of one embodiment of the presentinvention, the insulating film 114 or the insulating film 116 includesexcess oxygen. This structure can further reduce the change inelectrical characteristics of the transistor 100 due to lightirradiation.

Here, the oxide semiconductor film 108 is described in detail withreference to FIG. 20B.

FIG. 20B is a cross-sectional enlarged view of the oxide semiconductorfilm 108 and the vicinity thereof in the transistor 100 illustrated inFIG. 20C.

In FIG. 20B, t1, t2-1, and t2-2 denote a thickness of the oxidesemiconductor film 108 a, one thickness of the oxide semiconductor film108 b, and the other thickness the oxide semiconductor film 108 b,respectively. The oxide semiconductor film 108 b over the oxidesemiconductor film 108 a prevents the oxide semiconductor film 108 afrom being exposed to an etching gas, an etchant, or the like when theconductive films 112 a and 112 b are formed. This is why the oxidesemiconductor film 108 a is not or is hardly reduced in thickness. Incontrast, in the oxide semiconductor film 108 b, a portion notoverlapping with the conductive films 112 a and 112 b is etched byformation of the conductive films 112 a and 112 b, so that a depressionis formed in the etched region. In other words, a thickness of the oxidesemiconductor film 108 b in a region overlapping with the conductivefilms 112 a and 112 b is t2-1, and a thickness of the oxidesemiconductor film 108 b in a region not overlapping with the conductivefilms 112 a and 112 b is t2-2.

As for the relationships between the thicknesses of the oxidesemiconductor film 108 a and the oxide semiconductor film 108 b,t2-1>t1>t2-2 is preferable. A transistor with the thicknessrelationships can have high field-effect mobility and less variation inthreshold voltage in light irradiation.

When oxygen vacancy is formed in the oxide semiconductor film 108included in the transistor 100, electrons serving as carriers aregenerated; as a result, the transistor 100 tends to be normally-on.Therefore, for stable transistor characteristics, it is important toreduce oxygen vacancy in the oxide semiconductor film 108 particularlyoxygen vacancy in the oxide semiconductor film 108 a. In the structureof the transistor of one embodiment of the present invention, excessoxygen is introduced into an insulating film over the oxidesemiconductor film 108, here, the insulating film 114 and/or theinsulating film 116 over the oxide semiconductor film 108, wherebyoxygen is moved from the insulating film 114 and/or the insulating film116 to the oxide semiconductor film 108 to fill oxygen vacancy in theoxide semiconductor film 108 particularly in the oxide semiconductorfilm 108 a.

It is preferable that the insulating films 114 and 116 each include aregion (oxygen excess region) including oxygen in excess of that in thestoichiometric composition. In other words, the insulating films 114 and116 are insulating films capable of releasing oxygen. Note that theoxygen excess region is formed in the insulating films 114 and 116 insuch a manner that oxygen is introduced into the insulating films 114and 116 after the deposition, for example. As a method for introducingoxygen, an ion implantation method, an ion doping method, a plasmaimmersion ion implantation method, plasma treatment, or the like may beemployed.

In order to fill oxygen vacancy in the oxide semiconductor film 108 a,the thickness of the portion including the channel region and thevicinity of the channel region in the oxide semiconductor film 108 b ispreferably small, and t2-2<t1 is preferably satisfied. For example, thethickness of the portion including the channel region and the vicinityof the channel region in the oxide semiconductor film 108 b ispreferably more than or equal to 1 nm and less than or equal to 20 nm,more preferably more than or equal to 3 nm and less than or equal to 10nm.

Other constituent elements of the semiconductor device of thisembodiment are described below in detail.

<<Substrate>>

There is no particular limitation on the property of a material and thelike of the substrate 102 as long as the material has heat resistanceenough to withstand at least heat treatment to be performed later. Forexample, a glass substrate, a ceramic substrate, a quartz substrate, ora sapphire substrate may be used as the substrate 102.

Alternatively, a single crystal semiconductor substrate or apolycrystalline semiconductor substrate of silicon or silicon carbide, acompound semiconductor substrate of silicon germanium, an SOI substrate,or the like can be used as the substrate 102.

Alternatively, any of these substrates provided with a semiconductorelement, an insulating film, or the like may be used as the substrate102.

In the case where a glass substrate is used as the substrate 102, alarge substrate having any of the following sizes can be used: the 6thgeneration (1500 mm×1850 mm), the 7th generation (1870 mm×2200 mm), the8th generation (2200 mm×2400 mm), the 9th generation (2400 mm×2800 mm),and the 10th generation (2950 mm×3400 mm). Thus, a large display devicecan be manufactured.

Alternatively, a flexible substrate may be used as the substrate 102,and the transistor 100 may be provided directly on the flexiblesubstrate. Alternatively, a separation layer may be provided between thesubstrate 102 and the transistor 100. The separation layer can be usedwhen part or the whole of a semiconductor device formed over theseparation layer is separated from the substrate 102 and transferredonto another substrate. In such a case, the transistor 100 can betransferred to a substrate having low heat resistance or a flexiblesubstrate as well.

<<Conductive Film Functioning as Gate Electrode and Source and DrainElectrodes>>

The conductive film 104 functioning as a gate electrode and theconductive films 112 a and 112 b functioning as a source electrode and adrain electrode, respectively, can each be formed using a metal elementselected from chromium (Cr), copper (Cu), aluminum (Al), gold (Au),silver (Ag), zinc (Zn), molybdenum (Mo), tantalum (Ta), titanium (Ti),tungsten (W), manganese (Mn), nickel (Ni), iron (Fe), and cobalt (Co);an alloy including any of these metal element as its component; an alloyincluding a combination of any of these metal elements; or the like.

Furthermore, the conductive films 104, 112 a, and 112 b may have asingle-layer structure or a stacked-layer structure of two or morelayers. For example, a single-layer structure of an aluminum filmincluding silicon, a two-layer structure in which a titanium film isstacked over an aluminum film, a two-layer structure in which a titaniumfilm is stacked over a titanium nitride film, a two-layer structure inwhich a tungsten film is stacked over a titanium nitride film, atwo-layer structure in which a tungsten film is stacked over a tantalumnitride film or a tungsten nitride film, and a three-layer structure inwhich a titanium film, an aluminum film, and a titanium film are stackedin this order can be given. Alternatively, an alloy film or a nitridefilm in which aluminum and one or more elements selected from titanium,tantalum, tungsten, molybdenum, chromium, neodymium, and scandium arecombined may be used.

The conductive films 104, 112 a, and 112 b can be formed using alight-transmitting conductive material such as indium tin oxide, indiumoxide including tungsten oxide, indium zinc oxide including tungstenoxide, indium oxide including titanium oxide, indium tin oxide includingtitanium oxide, indium zinc oxide, or indium tin oxide to which siliconoxide is added.

A Cu—X alloy film (X is Mn, Ni, Cr, Fe, Co, Mo, Ta, or Ti) may be usedfor the conductive films 104, 112 a, and 112 b. Use of a Cu—X alloy filmenables the manufacturing cost to be reduced because wet etching processcan be used in the processing.

<<Insulating Film Functioning as Gate Insulating Film>>

As each of the insulating films 106 and 107 functioning as gateinsulating films of the transistor 100, an insulating film including atleast one of the following films formed by a plasma enhanced chemicalvapor deposition (PECVD) method, a sputtering method, or the like can beused: a silicon oxide film, a silicon oxynitride film, a silicon nitrideoxide film, a silicon nitride film, an aluminum oxide film, a hafniumoxide film, an yttrium oxide film, a zirconium oxide film, a galliumoxide film, a tantalum oxide film, a magnesium oxide film, a lanthanumoxide film, a cerium oxide film, and a neodymium oxide film Note thatinstead of a stacked-layer structure of the insulating films 106 and107, an insulating film of a single layer formed using a materialselected from the above or an insulating film of three or more layersmay be used.

The insulating film 106 has a function as a blocking film which inhibitspenetration of oxygen. For example, in the case where excess oxygen issupplied to the insulating film 107, the insulating film 114, theinsulating film 116, and/or the oxide semiconductor film 108, theinsulating film 106 can inhibit penetration of oxygen.

Note that the insulating film 107 that is in contact with the oxidesemiconductor film 108 functioning as a channel region of the transistor100 is preferably an oxide insulating film and preferably includes aregion including oxygen in excess of the stoichiometric composition(oxygen-excess region). In other words, the insulating film 107 is aninsulating film capable of releasing oxygen. In order to provide theoxygen excess region in the insulating film 107, the insulating film 107is formed in an oxygen atmosphere, for example. Alternatively, theoxygen excess region may be formed by introduction of oxygen into theinsulating film 107 after the deposition. As a method for introducingoxygen, an ion implantation method, an ion doping method, a plasmaimmersion ion implantation method, plasma treatment, or the like may beemployed.

In the case where hafnium oxide is used for the insulating film 107, thefollowing effect is attained. Hafnium oxide has a higher dielectricconstant than silicon oxide and silicon oxynitride. Therefore, by usinghafnium oxide, the thickness of the insulating film 107 can be madelarge as compared with the case where silicon oxide is used; thus,leakage current due to tunnel current can be low. That is, it ispossible to provide a transistor with a low off-state current. Moreover,hafnium oxide with a crystalline structure has higher dielectricconstant than hafnium oxide with an amorphous structure. Therefore, itis preferable to use hafnium oxide with a crystalline structure in orderto provide a transistor with a low off-state current. Examples of thecrystalline structure include a monoclinic crystal structure and a cubiccrystal structure. Note that one embodiment of the present invention isnot limited thereto.

In this embodiment, a silicon nitride film is formed as the insulatingfilm 106, and a silicon oxide film is formed as the insulating film 107.The silicon nitride film has a higher dielectric constant than a siliconoxide film and needs a larger thickness for capacitance equivalent tothat of the silicon oxide film. Thus, when the silicon nitride film isincluded in the gate insulating film of the transistor 100, the physicalthickness of the insulating film can be increased. This makes itpossible to reduce a decrease in withstand voltage of the transistor 100and furthermore to increase the withstand voltage, thereby reducingelectrostatic discharge damage to the transistor 100.

<<Oxide Semiconductor Film>>

The oxide semiconductor film 108 can be formed using the materialsdescribed above.

In the case where the oxide semiconductor film 108 includes In-M-Znoxide, it is preferable that the atomic ratio of metal elements of asputtering target used for forming the In-M-Zn oxide satisfy In≥M andZn≥M. As the atomic ratio of metal elements of such a sputtering target,InM:Zn=1:1:1, In:M:Zn=1:1:1.2, InM:Zn=2:1:3, InM:Zn=3:1:2, andInM:Zn=4:2:4.1 are preferable.

In the case where the oxide semiconductor film 108 is formed of In-M-Znoxide, it is preferable to use a target including polycrystallineIn-M-Zn oxide as the sputtering target. The use of the target includingpolycrystalline In-M-Zn oxide facilitates formation of the oxidesemiconductor film 108 having crystallinity. Note that the atomic ratiosof metal elements in the formed oxide semiconductor film 108 vary fromthe above atomic ratio of metal elements of the sputtering target withina range of ±40% as an error. For example, when a sputtering target withan atomic ratio of In to Ga and Zn of 4:2:4.1 is used, the atomic ratioof In to Ga and Zn in the oxide semiconductor film 108 may be 4:2:3 orin the vicinity of 4:2:3.

The oxide semiconductor film 108 a can be formed using the sputteringtarget having an atomic ratio of InM:Zn=2:1:3, InM:Zn=3:1:2, orIn:M:Zn=4:2:4.1. The oxide semiconductor film 108 b can be formed usingthe sputtering target having an atomic ratio of InM:Zn=1:1:1 orInM:Zn=1:1:1.2. Note that the atomic ratio of metal elements in asputtering target used for forming the oxide semiconductor film 108 bdoes not necessarily satisfy In≥M and Zn≥M, and may satisfy In≥M andZn<M, such as In:M:Zn=1:3:2.

The energy gap of the oxide semiconductor film 108 is 2 eV or more,preferably 2.5 eV or more, further preferably 3 eV or more. The use ofan oxide semiconductor having a wide energy gap can reduce off-statecurrent of the transistor 100. In particular, an oxide semiconductorfilm having an energy gap more than or equal to 2 eV, preferably morethan or equal to 2 eV and less than or equal to 3.0 eV is preferablyused as the oxide semiconductor film 108 a, and an oxide semiconductorfilm having an energy gap more than or equal to 2.5 eV and less than orequal to 3.5 eV is preferably used as the oxide semiconductor film 108b. Furthermore, the oxide semiconductor film 108 b preferably has ahigher energy gap than that of the oxide semiconductor film 108 a.

Each thickness of the oxide semiconductor film 108 a and the oxidesemiconductor film 108 b is more than or equal to 3 nm and less than orequal to 200 nm, preferably more than or equal to 3 nm and less than orequal to 100 nm, more preferably more than or equal to 3 nm and lessthan or equal to 50 nm. Note that the above-described thicknessrelationships between them are preferably satisfied.

An oxide semiconductor film with low carrier density is used as theoxide semiconductor film 108 b. For example, the carrier density of theoxide semiconductor film 108 b is lower than or equal to 1×10¹⁷/cm³,preferably lower than or equal to 1×10¹⁵/cm³, further preferably lowerthan or equal to 1×10¹³/cm³, still further preferably lower than orequal to 1×10¹¹/cm³.

Note that, without limitation to the compositions and materialsdescribed above, a material with an appropriate composition may be useddepending on required semiconductor characteristics and electricalcharacteristics (e.g., field-effect mobility and threshold voltage) of atransistor. Further, in order to obtain required semiconductorcharacteristics of a transistor, it is preferable that the carrierdensity, the impurity concentration, the defect density, the atomicratio of a metal element to oxygen, the interatomic distance, thedensity, and the like of the oxide semiconductor film 108 a and theoxide semiconductor film 108 b be set to be appropriate.

Note that it is preferable to use, as the oxide semiconductor film 108 aand the oxide semiconductor film 108 b, an oxide semiconductor film inwhich the impurity concentration is low and the density of defect statesis low, in which case the transistor can have more excellent electricalcharacteristics. Here, the state in which the impurity concentration islow and the density of defect states is low (the amount of oxygenvacancy is small) is referred to as “highly purified intrinsic” or“substantially highly purified intrinsic”. A highly purified intrinsicor substantially highly purified intrinsic oxide semiconductor film hasfew carrier generation sources, and thus can have a low carrier density.Thus, a transistor in which a channel region is formed in the oxidesemiconductor film rarely has a negative threshold voltage (is rarelynormally on). A highly purified intrinsic or substantially highlypurified intrinsic oxide semiconductor film has a low density of defectstates and accordingly has few carrier traps in some cases. Further, thehighly purified intrinsic or substantially highly purified intrinsicoxide semiconductor film has an extremely low off-state current; evenwhen an element has a channel width of 1×10⁶ μm and a channel length of10 μm, the off-state current can be less than or equal to themeasurement limit of a semiconductor parameter analyzer, that is, lessthan or equal to 1×10⁻¹³ A, at a voltage (drain voltage) between asource electrode and a drain electrode of from 1 V to 10 V.

Accordingly, the transistor in which the channel region is formed in thehighly purified intrinsic or substantially highly purified intrinsicoxide semiconductor film can have a small change in electricalcharacteristics and high reliability. Charges trapped by the trap statesin the oxide semiconductor film take a long time to be released and maybehave like fixed charges. Thus, the transistor whose channel region isformed in the oxide semiconductor film having a high density of trapstates has unstable electrical characteristics in some cases. Asexamples of the impurities, hydrogen, nitrogen, alkali metal, alkalineearth metal, and the like are given.

Hydrogen included in the oxide semiconductor film reacts with oxygenbonded to a metal atom to be water, and also causes oxygen vacancy in alattice from which oxygen is released (or a portion from which oxygen isreleased). Due to entry of hydrogen into the oxygen vacancy, an electronserving as a carrier is generated in some cases. Furthermore, in somecases, bonding of part of hydrogen to oxygen bonded to a metal atomcauses generation of an electron serving as a carrier. Thus, atransistor including an oxide semiconductor film which contains hydrogenis likely to be normally on. Accordingly, it is preferable that hydrogenbe reduced as much as possible in the oxide semiconductor film 108.Specifically, in the oxide semiconductor film 108, the concentration ofhydrogen which is measured by SIMS is lower than or equal to 2×10²⁰atoms/cm³, preferably lower than or equal to 5×10¹⁹ atoms/cm³, furtherpreferably lower than or equal to 1×10¹⁹ atoms/cm³, further preferablylower than or equal to 5×10¹⁸ atoms/cm³, further preferably lower thanor equal to 1×10¹⁸ atoms/cm³, further preferably lower than or equal to5×10¹⁷ atoms/cm³, and further preferably lower than or equal to 1×10¹⁶atoms/cm³.

When silicon or carbon that is one of elements belonging to Group 14 isincluded in the first oxide semiconductor film 108 a, oxygen vacancy isincreased in the first oxide semiconductor film 108 a, and the firstoxide semiconductor film 108 a becomes an n-type film. Thus, theconcentration of silicon or carbon (the concentration is measured bySIMS) in the first oxide semiconductor film 108 a or the concentrationof silicon or carbon (the concentration is measured by SIMS) in thevicinity of an interface with the oxide semiconductor film 108 a is setto be lower than or equal to 2×10¹⁸ atoms/cm³, preferably lower than orequal to 2×10¹⁷ atoms/cm³.

In addition, the concentration of alkali metal or alkaline earth metalof the first oxide semiconductor film 108 a, which is measured by SIMS,is lower than or equal to 1×10¹⁸ atoms/cm³, preferably lower than orequal to 2×10¹⁶ atoms/cm³. Alkali metal and alkaline earth metal mightgenerate carriers when bonded to an oxide semiconductor, in which casethe off-state current of the transistor might be increased. Therefore,it is preferable to reduce the concentration of alkali metal or alkalineearth metal of the oxide semiconductor film 108 a.

Furthermore, when including nitrogen, the oxide semiconductor film 108 aeasily becomes n-type by generation of electrons serving as carriers andan increase of carrier density. Thus, a transistor including an oxidesemiconductor film which contains nitrogen is likely to have normally-oncharacteristics. For this reason, nitrogen in the oxide semiconductorfilm is preferably reduced as much as possible; the concentration ofnitrogen which is measured by SIMS is preferably set to be, for example,lower than or equal to 5×10¹⁸ atoms/cm³.

Each of the first and second oxide semiconductor films 108 a and 108 bmay have a non-single-crystal structure, for example. The non-singlecrystal structure includes a c-axis aligned crystalline oxidesemiconductor (CAAC-OS) which is described later, a polycrystallinestructure, a microcrystalline structure, or an amorphous structure, forexample. Among the non-single crystal structure, the amorphous structurehas the highest density of defect states, whereas CAAC-OS has the lowestdensity of defect states.

<<Insulating Film Functioning as Protective Insulating Film ofTransistor>>

The insulating films 114 and 116 each have a function of supplyingoxygen to the oxide semiconductor film 108. The insulating film 118 hasa function of a protective insulating film of the transistor 100. Theinsulating films 114 and 116 include oxygen. Furthermore, the insulatingfilm 114 is an insulating film which can transmit oxygen. The insulatingfilm 114 also functions as a film which relieves damage to the oxidesemiconductor film 108 at the time of forming the insulating film 116 ina later step.

A silicon oxide film, a silicon oxynitride film, or the like with athickness greater than or equal to 5 nm and less than or equal to 150nm, preferably greater than or equal to 5 nm and less than or equal to50 nm can be used as the insulating film 114.

In addition, it is preferable that the number of defects in theinsulating film 114 be small and typically, the spin densitycorresponding to a signal that appears at g=2.001 due to a dangling bondof silicon be lower than or equal to 3×10¹⁷ spins/cm³ by electron spinresonance (ESR) measurement. This is because if the density of defectsin the insulating film 114 is high, oxygen is bonded to the defects andthe amount of oxygen that transmits the insulating film 114 isdecreased.

Note that all oxygen entering the insulating film 114 from the outsidedoes not move to the outside of the insulating film 114 and some oxygenremains in the insulating film 114. Furthermore, movement of oxygenoccurs in the insulating film 114 in some cases in such a manner thatoxygen enters the insulating film 114 and oxygen included in theinsulating film 114 moves to the outside of the insulating film 114.When an oxide insulating film which can transmit oxygen is formed as theinsulating film 114, oxygen released from the insulating film 116provided over the insulating film 114 can be moved to the oxidesemiconductor film 108 through the insulating film 114.

Note that the insulating film 114 can be formed using an oxideinsulating film having a low density of states due to nitrogen oxide.Note that the density of states due to nitrogen oxide can be formedbetween the energy of the valence band maximum (E_(v_os)) and the energyof the conduction band minimum (E_(c_os)) of the oxide semiconductorfilm A silicon oxynitride film that releases less nitrogen oxide, analuminum oxynitride film that releases less nitrogen oxide, and the likecan be used as the above oxide insulating film.

Note that a silicon oxynitride film that releases less nitrogen oxide isa film of which the amount of released ammonia is larger than the amountof released nitrogen oxide in TDS analysis; the amount of releasedammonia is typically greater than or equal to 1×10¹⁸/cm³ and less thanor equal to 5×10¹⁹/cm³. Note that the amount of released ammonia is theamount of ammonia released by heat treatment with which the surfacetemperature of a film becomes higher than or equal to 50° C. and lowerthan or equal to 650° C., preferably higher than or equal to 50° C. andlower than or equal to 550° C.

Nitrogen oxide (NO_(x); x is greater than 0 and less than or equal to 2,preferably greater than or equal to 1 and less than or equal to 2),typically NO₂ or NO, forms levels in the insulating film 114, forexample. The level is positioned in the energy gap of the oxidesemiconductor film 108. Therefore, when nitrogen oxide is diffused tothe interface between the insulating film 114 and the oxidesemiconductor film 108, an electron is in some cases trapped by thelevel on the insulating film 114 side. As a result, the trapped electronremains in the vicinity of the interface between the insulating film 114and the oxide semiconductor film 108; thus, the threshold voltage of thetransistor is shifted in the positive direction.

Nitrogen oxide reacts with ammonia and oxygen in heat treatment. Sincenitrogen oxide included in the insulating film 114 reacts with ammoniaincluded in the insulating film 116 in heat treatment, nitrogen oxideincluded in the insulating film 114 is reduced. Therefore, an electronis hardly trapped at the vicinity of the interface between theinsulating film 114 and the oxide semiconductor film 108.

By using such an oxide insulating film, the insulating film 114 canreduce the shift in the threshold voltage of the transistor, which leadsto a smaller change in the electrical characteristics of the transistor.

Note that in an ESR spectrum at 100 K or lower of the insulating film114, by heat treatment of a manufacturing process of the transistor,typically heat treatment at a temperature higher than or equal to 300°C. and lower than 350° C., a first signal that appears at a g-factor ofgreater than or equal to 2.037 and less than or equal to 2.039, a secondsignal that appears at a g-factor of greater than or equal to 2.001 andless than or equal to 2.003, and a third signal that appears at ag-factor of greater than or equal to 1.964 and less than or equal to1.966 are observed. The split width of the first and second signals andthe split width of the second and third signals that are obtained by ESRmeasurement using an X-band are each approximately 5 mT. The sum of thespin densities of the first signal that appears at a g-factor of greaterthan or equal to 2.037 and less than or equal to 2.039, the secondsignal that appears at a g-factor of greater than or equal to 2.001 andless than or equal to 2.003, and the third signal that appears at ag-factor of greater than or equal to 1.964 and less than or equal to1.966 is lower than 1×10¹⁸ spins/cm³, typically higher than or equal to1×10¹⁷ spins/cm³ and lower than 1×10¹⁸ spins/cm³.

In the ESR spectrum at 100 K or lower, the first signal that appears ata g-factor of greater than or equal to 2.037 and less than or equal to2.039, the second signal that appears at a g-factor of greater than orequal to 2.001 and less than or equal to 2.003, and the third signalthat appears at a g-factor of greater than or equal to 1.964 and lessthan or equal to 1.966 correspond to signals attributed to nitrogenoxide (NO_(x); x is greater than 0 and less than or equal to 2,preferably greater than or equal to 1 and less than or equal to 2).Typical examples of nitrogen oxide include nitrogen monoxide andnitrogen dioxide. In other words, the lower the total spin density ofthe first signal that appears at a g-factor of greater than or equal to2.037 and less than or equal to 2.039, the second signal that appears ata g-factor of greater than or equal to 2.001 and less than or equal to2.003, and the third signal that appears at a g-factor of greater thanor equal to 1.964 and less than or equal to 1.966 is, the lower thecontent of nitrogen oxide in the oxide insulating film is.

The concentration of nitrogen of the above oxide insulating filmmeasured by SIMS is lower than or equal to 6×10²⁰ atoms/cm³.

The above oxide insulating film is formed by a PECVD method at a filmsurface temperature higher than or equal to 220° C. and lower than orequal to 350° C. using silane and dinitrogen monoxide, whereby a denseand hard film can be formed.

The insulating film 116 is formed using an oxide insulating film thatcontains oxygen in excess of that in the stoichiometric composition.Part of oxygen is released by heating from the oxide insulating filmincluding oxygen in excess of that in the stoichiometric composition.The oxide insulating film including oxygen in excess of that in thestoichiometric composition is an oxide insulating film of which theamount of released oxygen converted into oxygen atoms is greater than orequal to 1.0×10¹⁰ atoms/cm³, preferably greater than or equal to3.0×10²⁰ atoms/cm³ in TDS analysis. Note that the temperature of thefilm surface in the TDS analysis is preferably higher than or equal to100° C. and lower than or equal to 700° C., or higher than or equal to100° C. and lower than or equal to 500° C.

A silicon oxide film, a silicon oxynitride film, or the like with athickness greater than or equal to 30 nm and less than or equal to 500nm, preferably greater than or equal to 50 nm and less than or equal to400 nm can be used as the insulating film 116.

It is preferable that the number of defects in the insulating film 116be small, and typically the spin density corresponding to a signal whichappears at g=2.001 due to a dangling bond of silicon be lower than1.5×10¹⁸ spins/cm³, preferably lower than or equal to 1×10¹⁸ spins/cm³by ESR measurement. Note that the insulating film 116 is provided moreapart from the oxide semiconductor film 108 than the insulating film 114is; thus, the insulating film 116 may have higher density of defectsthan the insulating film 114.

Furthermore, the insulating films 114 and 116 can be formed usinginsulating films formed of the same kinds of materials; thus, a boundarybetween the insulating films 114 and 116 cannot be clearly observed insome cases. Thus, in this embodiment, the boundary between theinsulating films 114 and 116 is shown by a dashed line. Although atwo-layer structure of the insulating films 114 and 116 is described inthis embodiment, the present invention is not limited to this. Forexample, a single-layer structure of the insulating film 114 may beemployed.

The insulating film 118 includes nitrogen. Alternatively, the insulatingfilm 118 includes nitrogen and silicon. The insulating film 118 has afunction of blocking oxygen, hydrogen, water, alkali metal, alkalineearth metal, or the like. It is possible to prevent outward diffusion ofoxygen from the oxide semiconductor film 108, outward diffusion ofoxygen included in the insulating films 114 and 116, and entry ofhydrogen, water, or the like into the oxide semiconductor film 108 fromthe outside by providing the insulating film 118. A nitride insulatingfilm, for example, can be used as the insulating film 118. The nitrideinsulating film is formed using silicon nitride, silicon nitride oxide,aluminum nitride, aluminum nitride oxide, or the like. Note that insteadof the nitride insulating film having a blocking effect against oxygen,hydrogen, water, alkali metal, alkaline earth metal, and the like, anoxide insulating film having a blocking effect against oxygen, hydrogen,water, and the like may be provided. As the oxide insulating film havinga blocking effect against oxygen, hydrogen, water, and the like, analuminum oxide film, an aluminum oxynitride film, a gallium oxide film,a gallium oxynitride film, an yttrium oxide film, an yttrium oxynitridefilm, a hafnium oxide film, a hafnium oxynitride film, and the like canbe given.

Although the variety of films such as the conductive films, theinsulating films, and the oxide semiconductor films which are describedabove can be formed by a sputtering method or a PECVD method, such filmsmay be formed by another method, e.g., a thermal CVD method. Examples ofthe thermal CVD method include a metal organic chemical vapor deposition(MOCVD) method and an atomic layer deposition (ALD) method.

A thermal CVD method has an advantage that no defect due to plasmadamage is generated since it does not utilize plasma for forming a film.

Deposition by a thermal CVD method may be performed in such a mannerthat a source gas and an oxidizer are supplied to the chamber at a timeso that the pressure in a chamber is set to an atmospheric pressure or areduced pressure, and react with each other in the vicinity of thesubstrate or over the substrate.

Deposition by an ALD method may be performed in such a manner that thepressure in a chamber is set to an atmospheric pressure or a reducedpressure, source gases for reaction are sequentially introduced into thechamber, and then the sequence of the gas introduction is repeated. Forexample, two or more kinds of source gases are sequentially supplied tothe chamber by switching respective switching valves (also referred toas high-speed valves). For example, a first source gas is introduced, aninert gas (e.g., argon or nitrogen) or the like is introduced at thesame time as or after the introduction of the first gas so that thesource gases are not mixed, and then a second source gas is introduced.Note that in the case where the first source gas and the inert gas areintroduced at a time, the inert gas serves as a carrier gas, and theinert gas may also be introduced at the same time as the introduction ofthe second source gas. Alternatively, the first source gas may beexhausted by vacuum evacuation instead of the introduction of the inertgas, and then the second source gas may be introduced. The first sourcegas is adsorbed on the surface of the substrate to form a first layer;then the second source gas is introduced to react with the first layer;as a result, a second layer is stacked over the first layer, so that athin film is formed. The sequence of the gas introduction is repeatedplural times until a desired thickness is obtained, whereby a thin filmwith excellent step coverage can be formed. The thickness of the thinfilm can be adjusted by the number of repetition times of the sequenceof the gas introduction; therefore, an ALD method makes it possible toaccurately adjust a thickness and thus is suitable for manufacturing aminute FET.

The variety of films such as the conductive films, the insulating films,the oxide semiconductor films, and the metal oxide films in thisembodiment can be formed by a thermal CVD method such as an MOCVD methodor an ALD method. For example, in the case where an In—Ga—Zn—O film isformed, trimethylindium, trimethylgallium, and dimethylzinc are used.Note that the chemical formula of trimethylindium is In(CH₃)₃. Thechemical formula of trimethylgallium is Ga(CH₃)₃. The chemical formulaof dimethylzinc is Zn(CH₃)₂. Without limitation to the abovecombination, triethylgallium (chemical formula: Ga(C₂H₅)₃) can be usedinstead of trimethylgallium and diethylzinc (chemical formula:Zn(C₂H₅)₂) can be used instead of dimethylzinc.

For example, in the case where a hafnium oxide film is formed by adeposition apparatus using an ALD method, two kinds of gases, that is,ozone (O₃) as an oxidizer and a source gas which is obtained byvaporizing liquid containing a solvent and a hafnium precursor compound(e.g., a hafnium alkoxide or a hafnium amide such astetrakis(dimethylamide)hafnium (TDMAH)) are used. Note that the chemicalformula of tetrakis(dimethylamide)hafnium is Hf[N(CH₃)₂]₄. Examples ofanother material liquid include tetrakis(ethylmethylamide)hafnium.

For example, in the case where an aluminum oxide film is formed by adeposition apparatus using an ALD method, two kinds of gases, e.g., H₂Oas an oxidizer and a source gas which is obtained by vaporizing liquidcontaining a solvent and an aluminum precursor compound (e.g.,trimethylaluminum (TMA)) are used. Note that the chemical formula oftrimethylaluminum is Al(CH₃)₃. Examples of another material liquidinclude tris(dimethylamide)aluminum, triisobutylaluminum, and aluminumtris(2,2,6,6-tetramethyl-3,5-heptanedionate).

For example, in the case where a silicon oxide film is formed by adeposition apparatus using an ALD method, hexachlorodisilane is adsorbedon a surface where a film is to be formed, chlorine included in theadsorbate is removed, and radicals of an oxidizing gas (e.g., O₂ ordinitrogen monoxide) are supplied to react with the adsorbate.

For example, in the case where a tungsten film is formed using adeposition apparatus using an ALD method, a WF₆ gas and a B₂H₆ gas aresequentially introduced plural times to form an initial tungsten film,and then a WF₆ gas and an H₂ gas are used, so that a tungsten film isformed. Note that an SiH₄ gas may be used instead of a B₂H₆ gas.

For example, in the case where an oxide semiconductor film, e.g., anIn—Ga—Zn—O film is formed using a deposition apparatus using an ALDmethod, an In(CH₃)₃ gas and an O₃ gas) are sequentially introducedplural times to form an InO layer, a GaO layer is formed using aGa(CH₃)₃ gas and an O₃ gas), and then a ZnO layer is formed using aZn(CH₃)₂ gas and an O₃ gas). Note that the order of these layers is notlimited to this example. A mixed compound layer such as an In—Ga—Olayer, an In—Zn-0 layer, or a Ga—Zn—O layer may be formed by mixingthese gases. Note that although an H₂O gas which is obtained by bubblingwater with an inert gas such as Ar may be used instead of an O₃ gas), itis preferable to use an O₃ gas), which does not contain H. Furthermore,instead of an In(CH₃)₃ gas, an In(C₂H₅)₃ gas may be used. Instead of aGa(CH₃)₃ gas, a Ga(C₂H₅)₃ gas may be used. Furthermore, a Zn(CH₃)₂ gasmay be used.

This embodiment can be combined with any of the other embodiments inthis specification as appropriate.

Embodiment 5

In this embodiment, structures of a transistor that can be used in thedisplay panel of one embodiment of the present invention will bedescribed with reference to FIGS. 21A to 21C.

<Structure Example of Semiconductor Device>

FIG. 21A is a top view of the transistor 100. FIG. 21B is across-sectional view taken along the cutting plane line X1-X2 in FIG.10A, and FIG. 21C is a cross-sectional view taken along the cuttingplane line Y1-Y2 in FIG. 10A. Note that in FIG. 21A, some components ofthe transistor 100 (e.g., an insulating film serving as a gateinsulating film) are not illustrated to avoid complexity. Furthermore,the direction of the cutting plane line X1-X2 may be called a channellength direction, and the direction of the cutting plane line Y1-Y2 maybe called a channel width direction. As in FIG. 21A, some components arenot illustrated in some cases in top views of transistors describedbelow.

The transistor 100 can be used for the display panel described inEmbodiment 1 or 2, or the like.

For example, when the transistor 100 is used as the transistor MD, thesubstrate 102, the conductive film 104, a stacked film of the insulatingfilm 106 and the insulating film 107, the oxide semiconductor film 108,the conductive film 112 a, the conductive film 112 b, a stacked film ofthe insulating film 114 and the insulating film 116, the insulating film118, and a conductive film 120 b can be referred to as the insulatingfilm 501C, the conductive film 504, the insulating film 506, thesemiconductor film 508, the conductive film 512A, the conductive film512B, the insulating film 516, the insulating film 518, and theconductive film 524, respectively.

The transistor 100 includes a conductive film 104 functioning as a firstgate electrode over a substrate 102, an insulating film 106 over thesubstrate 102 and the conductive film 104, an insulating film 107 overthe insulating film 106, an oxide semiconductor film 108 over theinsulating film 107, and conductive films 112 a and 112 b functioning assource and drain electrodes electrically connected to the oxidesemiconductor film 108, the insulating films 114 and 116 over the oxidesemiconductor film 108 and the conductive films 112 a and 112 b, aconductive film 120 a that is over the insulating film 116 andelectrically connected to the conductive film 112 b, the conductive film120 b over the insulating film 116, and the insulating film 118 over theinsulating film 116 and the conductive films 120 a and 120 b.

The insulating films 106 and 107 function as a first gate insulatingfilm of the transistor 100. The insulating films 114 and 116 function asa second gate insulating film of the transistor 100. The insulating film118 functions as a protective insulating film of the transistor 100. Inthis specification and the like, the insulating films 106 and 107 arecollectively referred to as a first insulating film, the insulatingfilms 114 and 116 are collectively referred to as a second insulatingfilm, and the insulating film 118 is referred to as a third insulatingfilm in some cases.

The conductive film 120 b can be used as a second gate electrode of thetransistor 100.

In the case where the transistor 100 is used in a display panel, theconductive film 120 a can be used as an electrode of a display element,or the like.

The oxide semiconductor film 108 includes the oxide semiconductor film108 b (on the conductive film 104 side) that functions as a first gateelectrode, and an oxide semiconductor film 108 c over the oxidesemiconductor film 108 b. The oxide semiconductor films 108 b and 108 ccontain In, M (M is Al, Ga, Y, or Sn), and Zn.

The oxide semiconductor film 108 b preferably includes a region in whichthe atomic proportion of In is larger than the atomic proportion of M,for example. The oxide semiconductor film 108 c preferably includes aregion in which the atomic proportion of In is smaller than that in theoxide semiconductor film 108 b.

The oxide semiconductor film 108 b including the region in which theatomic proportion of In is larger than that of M can increase thefield-effect mobility (also simply referred to as mobility or μFE) ofthe transistor 100. Specifically, the field-effect mobility of thetransistor 100 can exceed 10 cm²/Vs, preferably exceed 30 cm²/Vs.

For example, the use of the transistor with high field-effect mobilityfor a gate driver that generates a gate signal (specifically, ademultiplexer connected to an output terminal of a shift registerincluded in a gate driver) allows a semiconductor device or a displaydevice to have a narrow frame.

On the other hand, the oxide semiconductor film 108 b including theregion in which the atomic proportion of In is larger than that of Mmakes it easier to change electrical characteristics of the transistor100 in light irradiation. However, in the semiconductor device of oneembodiment of the present invention, the oxide semiconductor film 108 cis formed over the oxide semiconductor film 108 b. Furthermore, theoxide semiconductor film 108 c including the region in which the atomicproportion of In is smaller than that in the oxide semiconductor film108 b has larger Eg than the oxide semiconductor film 108 b. For thisreason, the oxide semiconductor film 108 which is a layered structure ofthe oxide semiconductor film 108 b and the oxide semiconductor film 108c has high resistance to a negative bias stress test with lightirradiation.

Impurities such as hydrogen or moisture entering the channel region ofthe oxide semiconductor film 108, particularly the oxide semiconductorfilm 108 b adversely affect the transistor characteristics and thereforecause a problem. Moreover, it is preferable that the amount ofimpurities such as hydrogen or moisture in the channel region of theoxide semiconductor film 108 b be as small as possible. Furthermore,oxygen vacancies formed in the channel region in the oxide semiconductorfilm 108 b adversely affect the transistor characteristics and thereforecause a problem. For example, oxygen vacancies formed in the channelregion in the oxide semiconductor film 108 b are bonded to hydrogen toserve as a carrier supply source. The carrier supply source generated inthe channel region in the oxide semiconductor film 108 b causes a changein the electrical characteristics, typically, shift in the thresholdvoltage, of the transistor 100 including the oxide semiconductor film108 b. Therefore, it is preferable that the amount of oxygen vacanciesin the channel region of the oxide semiconductor film 108 b be as smallas possible.

In view of this, one embodiment of the present invention is a structurein which insulating films in contact with the oxide semiconductor film108, specifically the insulating film 107 formed under the oxidesemiconductor film 108 and the insulating films 114 and 116 formed overthe oxide semiconductor film 108 include excess oxygen. Oxygen or excessoxygen is transferred from the insulating film 107 and the insulatingfilms 114 and 116 to the oxide semiconductor film 108, whereby theoxygen vacancies in the oxide semiconductor film can be reduced. As aresult, a change in electrical characteristics of the transistor 100,particularly a change in the transistor 100 due to light irradiation,can be reduced.

In one embodiment of the present invention, a manufacturing method isused in which the number of manufacturing steps is not increased or anincrease in the number of manufacturing steps is extremely small,because the insulating film 107 and the insulating films 114 and 116 aremade to contain excess oxygen. Thus, the transistors 100 can bemanufactured with high yield.

Specifically, in a step of forming the oxide semiconductor film 108 b,the oxide semiconductor film 108 b is formed by a sputtering method inan atmosphere containing an oxygen gas, whereby oxygen or excess oxygenis added to the insulating film 107 over which the oxide semiconductorfilm 108 b is formed.

Furthermore, in a step of forming the conductive films 120 a and 120 b,the conductive films 120 a and 120 b are formed by a sputtering methodin an atmosphere containing an oxygen gas, whereby oxygen or excessoxygen is added to the insulating film 116 over which the conductivefilms 120 a and 120 b are formed. Note that in some cases, oxygen orexcess oxygen is added also to the insulating film 114 and the oxidesemiconductor film 108 under the insulating film 116 when oxygen orexcess oxygen is added to the insulating film 116.

<Oxide Conductor>

Next, an oxide conductor is described. In a step of forming theconductive films 120 a and 120 b, the conductive films 120 a and 120 bserve as a protective film for suppressing release of oxygen from theinsulating films 114 and 116. The conductive films 120 a and 120 b serveas semiconductors before a step of forming the insulating film 118 andserve as conductors after the step of forming the insulating film 118.

To allow the conductive films 120 a and 120 b to serve as conductors, anoxygen vacancy is formed in the conductive films 120 a and 120 b andhydrogen is added from the insulating film 118 to the oxygen vacancy,whereby a donor level is formed in the vicinity of the conduction band.As a result, the conductivity of each of the conductive films 120 a and120 b is increased, so that the oxide semiconductor film becomes aconductor. The conductive films 120 a and 120 b having become conductorscan each be referred to as oxide conductor. Oxide semiconductorsgenerally have a visible light transmitting property because of theirlarge energy gap. An oxide conductor is an oxide semiconductor having adonor level in the vicinity of the conduction band. Therefore, theinfluence of absorption due to the donor level is small in an oxideconductor, and an oxide conductor has a visible light transmittingproperty comparable to that of an oxide semiconductor.

<Components of the Semiconductor Device>

Components of the semiconductor device of this embodiment will bedescribed below in detail.

As materials described below, materials described in Embodiment 4 can beused.

The material that can be used for the substrate 102 described inEmbodiment 4 can be used for the substrate 102 in this embodiment.Furthermore, the materials that can be used for the insulating films 106and 107 described in Embodiment 4 can be used for the insulating films106 and 107 in this embodiment.

In addition, the materials that can be used for the conductive filmsfunctioning as the gate electrode, the source electrode, and the drainelectrode described in Embodiment 4 can be used for the conductive filmsfunctioning as the first gate electrode, the source electrode, and thedrain electrode in this embodiment.

<<Oxide Semiconductor Film>>

The oxide semiconductor film 108 can be formed using the materialsdescribed above.

In the case where the oxide semiconductor film 108 b includes In-M-Znoxide, it is preferable that the atomic ratio of metal elements of asputtering target used for forming the In-M-Zn oxide satisfy In>M. Theatomic ratio between metal elements in such a sputtering target is, forexample, In:M:Zn=2:1:3, InM:Zn=3:1:2, or In:M:Zn=4:2:4.1.

In the case where the oxide semiconductor film 108 c is In-M-Zn oxide,it is preferable that the atomic ratio of metal elements of a sputteringtarget used for forming a film of the In-M-Zn oxide satisfy In≤M. Theatomic ratio of metal elements in such a sputtering target is, forexample, InM:Zn=1:1:1, In:M:Zn=1:1:1.2, InM:Zn=1:3:2, InM:Zn=1:3:4,InM:Zn=1:3:6, or InM:Zn=1:4:5.

In the case where the oxide semiconductor films 108 b and 108 c areformed of In-M-Zn oxide, it is preferable to use a target includingpolycrystalline In-M-Zn oxide as the sputtering target. The use of thetarget including polycrystalline In-M-Zn oxide facilitates formation ofthe oxide semiconductor films 108 b and 108 c having crystallinity. Notethat the atomic ratios of metal elements in each of the formed oxidesemiconductor films 108 b and 108 c vary from the above atomic ratio ofmetal elements of the sputtering target within a range of ±40% as anerror. For example, when a sputtering target of the oxide semiconductorfilm 108 b with an atomic ratio of In to Ga and Zn of 4:2:4.1 is used,the atomic ratio of In to Ga and Zn in the oxide semiconductor film 108b may be 4:2:3 or in the vicinity of 4:2:3.

The energy gap of the oxide semiconductor film 108 is 2 eV or more,preferably 2.5 eV or more, further preferably 3 eV or more. The use ofan oxide semiconductor having a wide energy gap can reduce off-statecurrent of the transistor 100. In particular, an oxide semiconductorfilm having an energy gap more than or equal to 2 eV, preferably morethan or equal to 2 eV and less than or equal to 3.0 eV is preferablyused as the oxide semiconductor film 108 b, and an oxide semiconductorfilm having an energy gap more than or equal to 2.5 eV and less than orequal to 3.5 eV is preferably used as the oxide semiconductor film 108c. Furthermore, the oxide semiconductor film 108 c preferably has ahigher energy gap than the oxide semiconductor film 108 b.

Each thickness of the oxide semiconductor film 108 b and the oxidesemiconductor film 108 c is more than or equal to 3 nm and less than orequal to 200 nm, preferably more than or equal to 3 nm and less than orequal to 100 nm, more preferably more than or equal to 3 nm and lessthan or equal to 50 nm.

An oxide semiconductor film with low carrier density is used as theoxide semiconductor film 108 c. For example, the carrier density of theoxide semiconductor film 108 c is lower than or equal to 1×10¹⁷/cm³,preferably lower than or equal to 1×10¹⁵/cm³, further preferably lowerthan or equal to 1×10¹³/cm³, still further preferably lower than orequal to 1×10¹¹/cm³.

Note that, without limitation to the compositions and materialsdescribed above, a material with an appropriate composition may be useddepending on required semiconductor characteristics and electricalcharacteristics (e.g., field-effect mobility and threshold voltage) of atransistor. Further, in order to obtain required semiconductorcharacteristics of a transistor, it is preferable that the carrierdensity, the impurity concentration, the defect density, the atomicratio of a metal element to oxygen, the interatomic distance, thedensity, and the like of the oxide semiconductor film 108 b and theoxide semiconductor film 108 c be set to be appropriate.

Note that it is preferable to use, as the oxide semiconductor film 108 band the oxide semiconductor film 108 c, an oxide semiconductor film inwhich the impurity concentration is low and the density of defect statesis low, in which case the transistor can have more excellent electricalcharacteristics. Here, the state in which the impurity concentration islow and the density of defect states is low (the amount of oxygenvacancy is small) is referred to as “highly purified intrinsic” or“substantially highly purified intrinsic”. A highly purified intrinsicor substantially highly purified intrinsic oxide semiconductor film hasfew carrier generation sources, and thus can have a low carrier density.Thus, a transistor in which a channel region is formed in the oxidesemiconductor film rarely has a negative threshold voltage (is rarelynormally on). A highly purified intrinsic or substantially highlypurified intrinsic oxide semiconductor film has a low density of defectstates and accordingly has few carrier traps in some cases. Further, thehighly purified intrinsic or substantially highly purified intrinsicoxide semiconductor film has an extremely low off-state current; evenwhen an element has a channel width of 1×10⁶ μm and a channel length of10 μm, the off-state current can be less than or equal to themeasurement limit of a semiconductor parameter analyzer, that is, lessthan or equal to 1×10⁻¹³ A, at a voltage (drain voltage) between asource electrode and a drain electrode of from 1 V to 10 V.

Accordingly, the transistor in which the channel region is formed in thehighly purified intrinsic or substantially highly purified intrinsicoxide semiconductor film can have a small change in electricalcharacteristics and high reliability. Charges trapped by the trap statesin the oxide semiconductor film take a long time to be released and maybehave like fixed charges. Thus, the transistor whose channel region isformed in the oxide semiconductor film having a high density of trapstates has unstable electrical characteristics in some cases. Asexamples of the impurities, hydrogen, nitrogen, alkali metal, andalkaline earth metal are given.

Hydrogen included in the oxide semiconductor film reacts with oxygenbonded to a metal atom to be water, and also causes oxygen vacancy in alattice from which oxygen is released (or a portion from which oxygen isreleased). Due to entry of hydrogen into the oxygen vacancy, an electronserving as a carrier is generated in some cases. Furthermore, in somecases, bonding of part of hydrogen to oxygen bonded to a metal atomcauses generation of an electron serving as a carrier. Thus, atransistor including an oxide semiconductor film which contains hydrogenis likely to be normally on. Accordingly, it is preferable that hydrogenbe reduced as much as possible in the oxide semiconductor film 108.Specifically, in the oxide semiconductor film 108, the concentration ofhydrogen which is measured by SIMS is lower than or equal to 2×10²⁰atoms/cm³, preferably lower than or equal to 5×10¹⁹ atoms/cm³, furtherpreferably lower than or equal to 1×10¹⁹ atoms/cm³, further preferablylower than or equal to 5×10¹⁸ atoms/cm³, further preferably lower thanor equal to 1×10¹⁸ atoms/cm³, further preferably lower than or equal to5×10¹⁷ atoms/cm³, and further preferably lower than or equal to 1×10¹⁶atoms/cm³.

The oxide semiconductor film 108 b preferably includes a region in whichhydrogen concentration is smaller than that in the oxide semiconductorfilm 108 c. A semiconductor device including the oxide semiconductorfilm 108 b having the region in which hydrogen concentration is smallerthan that in the oxide semiconductor film 108 c can be increased inreliability.

When silicon or carbon that is one of elements belonging to Group 14 isincluded in the oxide semiconductor film 108 b, oxygen vacancy isincreased in the oxide semiconductor film 108 b, and the oxidesemiconductor film 108 b becomes an n-type film. Thus, the concentrationof silicon or carbon (the concentration is measured by SIMS) in theoxide semiconductor film 108 b or the concentration of silicon or carbon(the concentration is measured by SIMS) in the vicinity of an interfacewith the oxide semiconductor film 108 b is set to be lower than or equalto 2×10¹⁸ atoms/cm³, preferably lower than or equal to 2×10¹⁷ atoms/cm³.

In addition, the concentration of alkali metal or alkaline earth metalof the oxide semiconductor film 108 b, which is measured by SIMS, islower than or equal to 1×10¹⁸ atoms/cm³, preferably lower than or equalto 2×10¹⁶ atoms/cm³. Alkali metal and alkaline earth metal mightgenerate carriers when bonded to an oxide semiconductor, in which casethe off-state current of the transistor might be increased. Therefore,it is preferable to reduce the concentration of alkali metal or alkalineearth metal of the oxide semiconductor film 108 b.

Furthermore, when including nitrogen, the oxide semiconductor film 108 beasily becomes n-type by generation of electrons serving as carriers andan increase of carrier density. Thus, a transistor including an oxidesemiconductor film which contains nitrogen is likely to have normally-oncharacteristics. For this reason, nitrogen in the oxide semiconductorfilm is preferably reduced as much as possible; the concentration ofnitrogen which is measured by SIMS is preferably set to be, for example,lower than or equal to 5×10¹⁸ atoms/cm³.

The oxide semiconductor film 108 b and the oxide semiconductor film 108c may have a non-single-crystal structure, for example. The non-singlecrystal structure includes a c-axis aligned crystalline oxidesemiconductor (CAAC-OS) which is described later, a polycrystallinestructure, a microcrystalline structure, or an amorphous structure, forexample. Among the non-single crystal structure, the amorphous structurehas the highest density of defect states, whereas CAAC-OS has the lowestdensity of defect states.

<<Insulating Films Functioning as Second Gate Insulating Film>>

The insulating films 114 and 116 function as a second gate insulatingfilm of the transistor 100. In addition, the insulating films 114 and116 each have a function of supplying oxygen to the oxide semiconductorfilm 108. That is, the insulating films 114 and 116 contain oxygen.Furthermore, the insulating film 114 is an insulating film which cantransmit oxygen. Note that the insulating film 114 also functions as afilm which relieves damage to the oxide semiconductor film 108 at thetime of forming the insulating film 116 in a later step.

For example, the insulating films 114 and 116 described in Embodiment 4can be used as the insulating films 114 and 116 in this embodiment.

<<Oxide Semiconductor Film Functioning as Conductive Film, OxideSemiconductor Film Functioning as Second Gate Electrode>>

The material of the oxide semiconductor film 108 described above can beused for the conductive film 120 a and the conductive film 120 bfunctioning as the second gate electrode.

That is, the conductive film 120 a and the conductive film 120 bfunctioning as a second gate electrode contain a metal element which isthe same as that contained in the oxide semiconductor film 108 (theoxide semiconductor film 108 b and the oxide semiconductor film 108 c).For example, the conductive film 120 b functioning as a second gateelectrode and the oxide semiconductor film 108 (the oxide semiconductorfilm 108 b and the oxide semiconductor film 108 c) contain the samemetal element; thus, the manufacturing cost can be reduced.

For example, in the case where the conductive film 120 a and theconductive film 120 b functioning as a second gate electrode are eachIn-M-Zn oxide, the atomic ratio of metal elements in a sputtering targetused for forming the In-M-Zn oxide preferably satisfies In≥M. The atomicratio of metal elements in such a sputtering target is InM:Zn=2:1:3,In:M:Zn=3:1:2, In:M:Zn=4:2:4.1, or the like.

The conductive film 120 a and the conductive film 120 b functioning as asecond gate electrode can each have a single-layer structure or astacked-layer structure of two or more layers. Note that in the casewhere the conductive film 120 a and the conductive film 120 b each havea stacked-layer structure, the composition of the sputtering target isnot limited to that described above.

<<Insulating Film Functioning as Protective Insulating Film ofTransistor>>

The insulating film 118 serves as a protective insulating film of thetransistor 100.

The insulating film 118 includes one or both of hydrogen and nitrogen.Alternatively, the insulating film 118 includes nitrogen and silicon.The insulating film 118 has a function of blocking oxygen, hydrogen,water, alkali metal, alkaline earth metal, or the like. It is possibleto prevent outward diffusion of oxygen from the oxide semiconductor film108, outward diffusion of oxygen included in the insulating films 114and 116, and entry of hydrogen, water, or the like into the oxidesemiconductor film 108 from the outside by providing the insulating film118.

The insulating film 118 has a function of supplying one or both ofhydrogen and nitrogen to the conductive film 120 a and the conductivefilm 120 b functioning as a second gate electrode. The insulating film118 preferably includes hydrogen and has a function of supplying thehydrogen to the conductive films 120 a and 120 b. The conductive films120 a and 120 b supplied with hydrogen from the insulating film 118function as conductors.

A nitride insulating film, for example, can be used as the insulatingfilm 118. The nitride insulating film is formed using silicon nitride,silicon nitride oxide, aluminum nitride, aluminum nitride oxide, or thelike.

Although the variety of films such as the conductive films, theinsulating films, and the oxide semiconductor films which are describedabove can be formed by a sputtering method or a PECVD method, such filmsmay be formed by another method, e.g., a thermal CVD method. Examples ofthe thermal CVD method include an MOCVD method and an ALD method.Specifically, the methods described in Embodiment 4 can be used.

This embodiment can be combined with any of the other embodiments inthis specification as appropriate.

Embodiment 6

In this embodiment, a structure of an input/output device which is oneembodiment of the present invention will be described with reference toFIG. 22.

FIG. 22 is an exploded view of an input/output device 800 forillustrating the components.

The input/output device 800 includes a display panel 806 and a touchsensor 804 having a region overlapping with the display panel 806. Notethat the input/output device 800 can be referred to as a touch panel.

The input/output device 800 is provided with a driver circuit 810 fordriving the touch sensor 804 and the display panel 806, a battery 811for supplying power to the driver circuit 810, and a housing where thetouch sensor 804, the display panel 806, the driver circuit 810, and thebattery 811 are stored.

<<Touch Sensor 804>>

The touch sensor 804 includes a region overlapping with the displaypanel 806. Note that an FPC 803 is electrically connected to the touchsensor 804.

For the touch sensor 804, a resistive touch sensor, a capacitive touchsensor, or a touch sensor using a photoelectric conversion element canbe used, for example.

Note that the touch sensor 804 may be used as part of the display panel806.

<<Display Panel 806>>

For example, the display panel described in Embodiment 1 or 2 can beused as the display panel 806. Note that an FPC 805 is electricallyconnected to the display panel 806.

<<Driver Circuit 810>>

As the driver circuit 810, a power supply circuit or a signal processingcircuit can be used, for example. Power supplied to the battery or anexternal commercial power supply can be utilized.

The signal processing circuit has a function of outputting a videosignal and a clock signal.

The power supply circuit has a function of supplying predeterminedpower.

<<Housing>>

An upper cover 801, a lower cover 802 which fits the upper cover 801,and a frame 809 which is stored in a region surrounded by the uppercover 801 and the lower cover 802 can be used for the housing, forexample.

The frame 809 has a function of protecting the display panel 806, and afunction of blocking electromagnetic waves generated by the operation ofthe driver circuit 810 or a function of a radiator plate.

Metal, a resin, an elastomer, or the like can be used for the uppercover 801, the lower cover 802, or the frame 809.

<<Battery 811>>

The battery 811 has a function of supplying power.

Note that a member such as a polarizing plate, a retardation plate, or aprism sheet can be used for the input/output device 800.

This embodiment can be combined with any of the other embodiments inthis specification as appropriate.

Embodiment 7

In this embodiment, a structure of an information processing device ofone embodiment of the present invention will be described with referenceto FIGS. 23A and 23B, FIGS. 24A to 24D, FIGS. 25A and 25B, and FIG. 26.

FIG. 23A is a block diagram illustrating a structure of an informationprocessing device 200. FIG. 23B is a projection view illustrating anexample of an external view of the information processing device 200.

FIG. 24A is a block diagram illustrating a configuration of a displayportion 230. FIG. 24B is a block diagram illustrating a configuration ofa display portion 230B. FIG. 24C is a circuit diagram illustrating aconfiguration of a pixel 232(i,j).

<Configuration Example of Information Processing Device>

The information processing device 200 described in this embodimentincludes an arithmetic device 210 and an input/output device 220 (seeFIG. 23A).

The arithmetic device 210 is configured to receive positionalinformation P1 and supply image information V and control information.

The input/output device 220 is configured to supply the positionalinformation P1 and receive the image information V and the controlinformation.

The input/output device 220 includes the display portion 230 thatdisplays the image information V and an input portion 240 that suppliesthe positional information P1.

The display portion 230 includes a first display element and a seconddisplay element overlapping with the opening in the reflective film ofthe first display element. The display portion 230 further includes afirst pixel circuit for driving the first display element and a secondpixel circuit for driving the second display element.

The input portion 240 is configured to detect the position of a pointerand supply the positional information P1 determined in accordance withthe position.

The arithmetic device 210 is configured to determine the moving speed ofthe pointer in accordance with the positional information P1.

The arithmetic device 210 is configured to determine the contrast orbrightness of the image information V in accordance with the movingspeed.

The information processing device 200 described in this embodimentincludes the input/output device 220 that supplies the positionalinformation P1 and receives the image information V and the arithmeticdevice 210 that receives the positional information P1 and supplies theimage information V. The arithmetic device 210 is configured todetermine the contrast or brightness of the image information V inaccordance with the moving speed of the positional information P1.

With this structure, eyestrain on a user caused when the displayposition of image information is moved can be reduced, that is,eye-friendly display can be achieved. Moreover, the power consumptioncan be reduced and excellent visibility can be provided even in a brightplace exposed to direct sunlight, for example. Thus, the novelinformation processing device that is highly convenient or reliable canbe provided.

<Configuration>

The information processing device of one embodiment of the presentinvention includes the arithmetic device 210 or the input/output device220.

<<Arithmetic Device 210>>

The arithmetic device 210 includes an arithmetic portion 211 and amemory portion 212. The arithmetic device 210 further includes atransmission path 214 and an input/output interface 215 (see FIG. 23A).

<<Arithmetic Portion 211>>

The arithmetic portion 211 is configured to, for example, execute aprogram. For example, a CPU described in Embodiment 8 can be used. Thus,power consumption can be sufficiently reduced.

<<Memory Portion 212>>

The memory portion 212 is configured to, for example, store the programexecuted by the arithmetic portion 211, initial information, settinginformation, an image, or the like.

Specifically, a hard disk, a flash memory, a memory including atransistor including an oxide semiconductor, or the like can be used forthe memory portion 212.

<<Input/Output Interface 215, Transmission Path 214>>

The input/output interface 215 includes a terminal or a wiring and isconfigured to supply and receive information. For example, theinput/output interface 215 can be electrically connected to thetransmission path 214 and the input/output device 220.

The transmission path 214 includes a wiring and is configured to supplyand receive information. For example, the transmission path 214 can beelectrically connected to the input/output interface 215. In addition,the transmission path 214 can be electrically connected to thearithmetic portion 211 or the memory portion 212.

<<Input/Output Device 220>>

The input/output device 220 includes the display portion 230, the inputportion 240, a sensor portion 250, or a communication portion 290.

<<Display Portion 230>>

The display portion 230 includes a display region 231, a driver circuitGD, and a driver circuit SD (see FIG. 24A). For example, the displaypanel described in Embodiment 1 or 2 can be used. Thus, low powerconsumption can be achieved.

The display region 231 includes a plurality of pixels 232(i, 1) to 232(i, n) arranged in the row direction, a plurality of pixels 232(1,j) to232 (m,j) arranged in the column direction, a scan line G(i)electrically connected to the pixels 232(i, 1) to 232 (i, n), and asignal line 5(j) electrically connected to the pixels 232(1,j) to 232(m,j). Note that i is an integer greater than or equal to 1 and lessthan or equal to m, j is an integer greater than or equal to 1 and lessthan or equal to n, and each of m and n is an integer greater than orequal to 1.

Note that the pixel 232(i,j) is electrically connected to the scan lineG1(i), the scan line G2(i), the signal line S(j), the wiring ANO, thewiring VCOM1, and the wiring VCOM2 (see FIG. 24C).

Note that the scan line G1(i) includes the scan line G1(i) and the scanline G2(i) (see FIGS. 24A and 24B).

The display portion can include a plurality of driver circuits. Forexample, the display portion 230B can include a driver circuit GDA and adriver circuit GDB (see FIG. 24B).

<<Driver Circuit GD>>

The driver circuit GD is configured to supply a selection signal inaccordance with the control information.

For example, the driver circuit GD is configured to supply a selectionsignal to one scan line at a frequency of 30 Hz or higher, preferably 60Hz or higher, in accordance with the control information. Accordingly,moving images can be smoothly displayed.

For example, the driver circuit GD is configured to supply a selectionsignal to one scan line at a frequency of lower than 30 Hz, preferablylower than 1 Hz, more preferably less than once per minute, inaccordance with the control information. Accordingly, a still image canbe displayed while flickering is suppressed.

For example, in the case where a plurality of driver circuits isprovided, the driver circuits GDA and GDB may supply the selectionsignals at different frequencies. Specifically, the selection signal canbe supplied at a higher frequency to a region on which moving images aresmoothly displayed than to a region on which a still image is displayedin a state where flickering is suppressed.

<<Driver Circuit SD>>

The driver circuit SD is configured to supply an image signal inaccordance with the image information V.

<<Pixel 232(i,j)>>

The pixel 232(i,j) includes a first display element 235LC and a seconddisplay element 235EL overlapping with the opening in the reflectivefilm of the first display element 235LC. The pixel 232(i,j) furtherincludes a first pixel circuit for driving the first display element235LC and a second pixel circuit for driving the second display element235EL (see FIG. 24C).

<<First Display Element 235LC>>

For example, a display element having a function of controlling lighttransmission can be used as the first display element 235LC.Specifically, a polarizing plate and a liquid crystal element, a MEMSshutter display element, or the like can be used.

Specifically, a liquid crystal element driven in any of the followingdriving modes can be used: an in-plane switching (IPS) mode, a twistednematic (TN) mode, a fringe field switching (FFS) mode, an axiallysymmetric aligned micro-cell (ASM) mode, an optically compensatedbirefringence (OCB) mode, a ferroelectric liquid crystal (FLC) mode, anantiferroelectric liquid crystal (AFLC) mode, and the like.

In addition, a liquid crystal element that can be driven by, forexample, a vertical alignment (VA) mode such as a multi-domain verticalalignment (MVA) mode, a patterned vertical alignment (PVA) mode, anelectrically controlled birefringence (ECB) mode, a continuous pinwheelalignment (CPA) mode, or an advanced super view (ASV) mode can be used.

The first display element 235LC includes a first electrode, a secondelectrode, and a liquid crystal layer. The liquid crystal layer containsa liquid crystal material whose orientation is controlled by voltageapplied between the first electrode and the second electrode. Forexample, the orientation of the liquid crystal material can becontrolled by an electric field in the thickness direction (alsoreferred to as the vertical direction), the horizontal direction, or thediagonal direction of the liquid crystal layer.

For example, thermotropic liquid crystal, low-molecular liquid crystal,high-molecular liquid crystal, polymer dispersed liquid crystal,ferroelectric liquid crystal, anti-ferroelectric liquid crystal, or thelike can be used. These liquid crystal materials exhibit a cholestericphase, a smectic phase, a cubic phase, a chiral nematic phase, anisotropic phase, or the like depending on conditions. Alternatively, aliquid crystal material that exhibits a blue phase can be used.

<<Second Display Element 235EL>>

A display element having a function of emitting light, such as anorganic EL element, can be used as the second display element 235EL.

Specifically, an organic EL element which emits white light can be usedas the second display element 235EL. Alternatively, an organic ELelement which emits blue light, green light, or red light can be used asthe second display element 235EL.

<<Pixel Circuit>>

A pixel circuit including a circuit which is configured to drive thefirst display element 235LC and/or the second display element 235EL canbe used.

For example, a pixel circuit which is electrically connected to the scanline G1(i), the scan line G2(i), the signal line SU), the wiring ANO,the wiring VCOM1, and the wiring VCOM2 and which drives a light-emittingelement and an organic EL element is described (see FIG. 24C).

Alternatively, for example, a switch, a transistor, a diode, a resistor,a capacitor, or an inductor can be used in the pixel circuit.

For example, one or a plurality of transistors can be used as a switch.Alternatively, a plurality of transistors connected in parallel, inseries, or in combination of parallel connection and series connectioncan be used as a switch.

For example, a capacitor may be formed by the first electrode of thefirst display element 235LC and a conductive film having a regionoverlapping with the first electrode.

For example, the pixel circuit includes a transistor functioning as theswitch SW1, the first display element 235LC, and the capacitor C1. Agate electrode of the transistor is electrically connected to the scanline G1 (i), and a first electrode of the transistor is electricallyconnected to the signal line S(j). A first electrode of the firstdisplay element 235LC is electrically connected to a second electrode ofthe transistor, and a second electrode of the first display element235LC is electrically connected to the wiring VCOM1. A first electrodeof the capacitor C1 is electrically connected to the second electrode ofthe transistor, and a second electrode of the capacitor C1 iselectrically connected to the wiring VCOM1.

The pixel circuit includes the transistor functioning as the switch SW2.A gate electrode of the transistor is electrically connected to the scanline G2(i), a first electrode of the transistor is electricallyconnected to the signal line S(j). In addition, the pixel circuitincludes the transistor M. A gate electrode of the transistor M iselectrically connected to a second electrode of the transistorfunctioning as the switch SW2. A first electrode of the transistor M iselectrically connected to the wiring ANO. In addition, the pixel circuitincludes the capacitor C2. A first electrode of the capacitor C2 iselectrically connected to the second electrode of the transistorfunctioning as the switch SW2. A second electrode of the capacitor C2 iselectrically connected to the second electrode of the transistor M. Inaddition, the pixel circuit includes a second display element 235EL. Afirst electrode and a second electrode of the second display element235EL are electrically connected to the second electrode of thetransistor M and the wiring VCOM2, respectively.

<<Transistor>>

For example, a semiconductor film formed at the same step can be usedfor transistors in the driver circuit and the pixel circuit.

As the transistors in the driver circuit and the pixel circuit,bottom-gate transistors, top-gate transistors, or the like can be used.

For example, a manufacturing line for a bottom-gate transistor includingamorphous silicon as a semiconductor can be easily remodeled into amanufacturing line for a bottom-gate transistor including an oxidesemiconductor as a semiconductor. Furthermore, for example, amanufacturing line for a top-gate transistor including polysilicon as asemiconductor can be easily remodeled into a manufacturing line for atop-gate transistor including an oxide semiconductor as a semiconductor.

For example, a transistor including a semiconductor containing anelement of Group 4 can be used. Specifically, a semiconductor containingsilicon can be used for a semiconductor film. For example, singlecrystal silicon, polysilicon, microcrystalline silicon, or amorphoussilicon can be used for the semiconductor of the transistor.

Note that the temperature for forming a transistor using polysilicon ina semiconductor is lower than the temperature for forming a transistorusing single crystal silicon in a semiconductor.

In addition, the transistor using polysilicon in a semiconductor hashigher field-effect mobility than the transistor using amorphous siliconin a semiconductor, and therefore a pixel including the transistor usingpolysilicon can have a high aperture ratio. Moreover, pixels arranged ata high density, a gate driver circuit, and a source driver circuit canbe formed over the same substrate. As a result, the number of componentsincluded in an electronic device can be reduced.

In addition, the transistor using polysilicon in a semiconductor hashigher reliability than the transistor using amorphous silicon in asemiconductor.

For example, a transistor including an oxide semiconductor can be used.Specifically, an oxide semiconductor containing indium or an oxidesemiconductor containing indium, gallium, and zinc can be used for asemiconductor film.

For example, a transistor having a lower leakage current in an off statethan a transistor that uses amorphous silicon for a semiconductor filmcan be used. Specifically, a transistor that uses an oxide semiconductorfor a semiconductor film can be used.

A pixel circuit in the transistor that uses an oxide semiconductor forthe semiconductor film can hold an image signal for a longer time than apixel circuit in a transistor that uses amorphous silicon for asemiconductor film Specifically, the selection signal can be supplied ata frequency of lower than 30 Hz, preferably lower than 1 Hz, morepreferably less than once per minute while flickering is suppressed.Consequently, eyestrain on a user of the information processing devicecan be reduced, and power consumption for driving can be reduced.

Alternatively, for example, a transistor including a compoundsemiconductor can be used. Specifically, a semiconductor containinggallium arsenide can be used for a semiconductor film.

For example, a transistor including an organic semiconductor can beused. Specifically, an organic semiconductor containing any ofpolyacenes and graphene can be used for the semiconductor film.

<<Input Portion 240>>

A variety of human interfaces or the like can be used as the inputportion 240 (see FIG. 23A).

For example, a keyboard, a mouse, a touch sensor, a microphone, acamera, or the like can be used as the input portion 240. Note that atouch sensor having a region overlapping with the display portion 230can be used. An input/output device that includes the display portion230 and a touch sensor having a region overlapping with the displayportion 230 can be referred to as a touch panel.

For example, a user can make various gestures (e.g., tap, drag, swipe,and pinch in) using his/her finger as a pointer on the touch panel.

The arithmetic device 210, for example, analyzes information on theposition, track, or the like of the finger on the touch panel anddetermines that a specific gesture is supplied when the analysis resultsmeet predetermined conditions. Therefore, the user can supply a certainoperation instruction associated with a certain gesture by using thegesture.

For instance, the user can supply a “scrolling instruction” for changinga portion where image information is displayed by using a gesture oftouching and moving his/her finger on the touch panel.

<<Sensor Portion 250>>

The sensor portion 250 is configured to acquire information P2 bymeasuring the surrounding state.

For example, a camera, an acceleration sensor, a direction sensor, apressure sensor, a temperature sensor, a humidity sensor, an illuminancesensor, or a global positioning system (GPS) signal receiving circuitcan be used as the sensor portion 250.

For example, when the arithmetic device 210 determines that the ambientlight level measured by an illuminance sensor of the sensor portion 250is sufficiently higher than the predetermined illuminance, image data isdisplayed using the first display element 235LC. When the arithmeticdevice 210 determines that it is dim, image data is displayed using thefirst display element 235LC and the second display element 235EL. Whenthe arithmetic device 210 determines that it is dark, image data isdisplayed using the second display element 235EL.

Specifically, an image is displayed with a reflective display elementand/or a self-luminous display element depending on the ambientbrightness. For example, a liquid crystal element and an organic ELelement can be used as the reflective display element and theself-luminous display element, respectively.

Thus, image information can be displayed in such a manner that, forexample, a reflective display element is used under strong ambientlight, a reflective display element and a self-luminous display elementare used in dim light, and a self-luminous display element is used indark light. Thus, a novel display device with high visibility and lowpower consumption can be provided. A novel data processor which ishighly convenient or reliable can be provided.

For example, a sensor measuring chromaticity of ambient light, such as aCCD camera, can be used in the sensor portion 250, white balance can beadjusted in accordance with the chromaticity of ambient light measuredby the sensor portion 250.

Specifically, in the first step, imbalance disruption of white balanceof ambient light is measured.

In the second step, the intensity of light of a color which isinsufficient in an image to be displayed by the first display elementusing reflection of ambient light is estimated.

In the third step, ambient light is reflected by the first displayelement, and light is emitted from the second display element so thatlight of the insufficient color is supplemented, whereby the image isdisplayed.

In this manner, display can be performed with adjusted white balance byutilizing light reflected by the first display element and light emittedfrom the second display element. Thus, a novel data processor which candisplay an image with low power consumption or with adjusted whitebalance and which is highly convenient and reliable can be provided.

<<Communication Portion 290>>

The communication portion 290 is configured to supply and acquireinformation to/from a network.

<<Program>>

A program of one embodiment of the present invention will be describedwith reference to FIGS. 25A and 25B and FIG. 26.

FIG. 25A is a flow chart showing main processing of the program of oneembodiment of the present invention, and FIG. 25B is a flow chartshowing interrupt processing.

FIG. 26 schematically illustrates a method for displaying imageinformation on the display portion 230.

The program of one embodiment of the present invention has the followingsteps (see FIG. 25A).

In a first step, setting is initialized (see (S1) in FIG. 25A).

For instance, predetermined image information and the second mode can beused for the initialization.

For example, a still image can be used as the predetermined imageinformation. Alternatively, a mode in which the selection signal issupplied at a frequency of lower than 30 Hz, preferably lower than 1 Hz,more preferably less than once per minute can be used as the secondmode. For example, in the case where the time is displayed on the dataprocessor on the second time scale, a mode in which the selection signalis supplied at a frequency of 1 Hz can be used as the second mode. Inthe case where the time is displayed on the data processor on the minutetime scale, a mode in which the selection signal is supplied once perminute can be used as the second mode.

In a second step, interrupt processing is allowed (see S2 in FIG. 25A).Note that an arithmetic device allowed to execute the interruptprocessing can perform the interrupt processing in parallel with themain processing. The arithmetic device which has returned from theinterrupt processing to the main processing can reflect the results ofthe interrupt processing in the main processing. For example, in thecase where the time is displayed on the information processing device onthe second time scale, a mode in which the selection signal is suppliedat a frequency of 1 Hz can be used as the second mode. In the case wherethe time is displayed on the information processing device on the minutetime scale, a mode in which the selection signal is supplied once perminute can be used as the second mode.

The arithmetic device may execute the interrupt processing when acounter has an initial value, and the counter may be set at a valueother than the initial value when the arithmetic device returns from theinterrupt processing. Thus, the interrupt processing is ready to beexecuted after the program is started up.

In a third step, image information is displayed in a mode selected inthe first step or the interrupt processing (see S3 in FIG. 25A).

For instance, predetermined image information is displayed in the secondmode, in accordance with the initialization.

Specifically, the predetermined image information is displayed in a modein which the selection signal is supplied to one scan line at afrequency of lower than 30 Hz, preferably lower than 1 Hz, morepreferably less than once per minute.

For example, the selection signal is supplied at Time T1 so that firstimage information PIC1 is displayed on the display portion 230 (see FIG.26). At Time T2, which is, for example, one second after Time T1, theselection signal is supplied so that the predetermined image informationis displayed.

Alternatively, in the case where a predetermined event is not suppliedin the interrupt processing, image information is displayed in thesecond mode.

For example, the selection signal is supplied at Time T5 so that fourthimage information PIC4 is displayed on the display portion 230. At TimeT6, which is, for example, one second after Time T5, the selectionsignal is supplied so that the same image information is displayed. Notethat the length of a period from Time T5 to Time T6 can be equal to thatof a period from Time Ti to Time T2.

For instance, in the case where the predetermined event is supplied inthe interrupt processing, predetermined image information is displayedin the first mode.

Specifically, in the case where an event associated with a “page turninginstruction” is supplied in the interrupt processing, image informationis switched from one to another in a mode in which the selection signalis supplied to one scan line at a frequency of 30 Hz or higher,preferably 60 Hz or higher.

Alternatively, in the case where an event associated with the “scrollinginstruction” is supplied in the interrupt processing, second imageinformation PIC2, which includes part of the displayed first imageinformation PIC1 and the following part, is displayed in a mode in whichthe selection signal is supplied to one scan line at a frequency of 30Hz or higher, preferably 60 Hz or higher.

Thus, for example, moving images in which images are gradually switchedin accordance with the “page turning instruction” can be displayedsmoothly. Alternatively, a moving image in which an image is graduallymoved in accordance with the “scrolling instruction” can be displayedsmoothly.

Specifically, the selection signal is supplied at Time T3 after theevent associated with the “scrolling instruction” is supplied so thatthe second image information PIC2 whose display position and the likeare changed from those of the first image information PIC1 is displayed(see FIG. 26). The selection signal is supplied at Time T4 so that thirdimage information PIC3 whose display position and the like are changedfrom those of the second image information PIC2 is displayed. Note thateach of a period from Time T2 to Time T3, a period from Time T3 to TimeT4, and a period from Time T4 to Time T5 is shorter than the period fromTime Ti to Time T2.

In the fourth step, the program moves to the fifth step when atermination instruction is supplied, and the program moves to the thirdstep when the termination instruction is not supplied (see S4 in FIG.25A).

Note that in the interrupt processing, for example, the terminationinstruction can be supplied.

In the fifth step, the program terminates (see S5 in FIG. 25A).

The interrupt processing includes sixth to eighth steps described below(see FIG. 25B).

In the sixth step, the processing proceeds to the seventh step when apredetermined event has been supplied, whereas the processing proceedsto the eighth step when the predetermined event has not been supplied(see S6 in FIG. 25B).

For example, whether the predetermined event is supplied in apredetermined period or not can be a branch condition. Specifically, thepredetermined period can be longer than 0 seconds and shorter than orequal to 5 seconds, preferably shorter than or equal to 1 second,further preferably shorter than or equal to 0.5 seconds, still furtherpreferably shorter than or equal to 0.1 seconds.

For example, the predetermined event can include an event associatedwith the termination instruction.

In the seventh step, the mode is changed (see S7 in FIG. 25B).Specifically, the mode is changed to the second mode when the first modehas been selected, or the mode is changed to the first mode when thesecond mode has been selected.

In the eighth step, the interrupt processing terminates (see S8 in FIG.25B).

<<Predetermined Event>>

A variety of instructions can be associated with a variety of events.

The following instructions can be given as examples: “page-turninginstruction” for switching displayed image information from one toanother and “scroll instruction” for moving the display position of partof image information and displaying another part continuing from thatpart.

For example, the following events can be used: events supplied using apointing device such as a mouse (e.g., “click” and “drag”) and eventssupplied to a touch panel with a finger or the like used as a pointer(e.g., “tap”, “drag”, and “swipe”).

For example, the position of a slide bar pointed by a pointer, the swipespeed, and the drag speed can be used as parameters assigned to aninstruction associated with the predetermined event.

Specifically, a parameter that determines the page-turning speed or thelike can be used to execute the “page-turning instruction,” and aparameter that determines the moving speed of the display position orthe like can be used to execute the “scroll instruction.”

For example, the display brightness, contrast, or saturation may bechanged in accordance with the page-turning speed and/or the scrollspeed.

Specifically, in the case where the page-turning speed and/or the scrollspeed are/is higher than the predetermined speed, the display brightnessmay be decreased in synchronization with the speed.

Alternatively, in the case where the page-turning speed and/or thescroll speed are/is higher than the predetermined speed, the contrastmay be decreased in synchronization with the speed.

For example, the speed at which user's eyes cannot follow displayedimages can be used as the predetermined speed.

The contrast can be reduced in such a manner that the gray level of abright region (with a high gray level) included in image information isbrought close to the gray level of a dark region (with a low gray level)included in the image information.

Alternatively, the contrast can be reduced in such a manner that thegray level of the dark region included in image information is broughtclose to the gray level of the bright region included in the imageinformation.

Specifically, in the case where the page-turning speed and/or the scrollspeed are/is higher than the predetermined speed, display may beperformed such that the yellow tone is increased or the blue tone isdecreased in synchronization with the speed.

Image information may be generated based on the usage ambience of theinformation processing device 200 acquired by the sensor portion 250.For example, a color selected from user's selections in accordance withthe acquired ambient brightness or the like can be used as thebackground color of the image information (see FIG. 23B). Thus,favorable environment can be provided for a user of the informationprocessing device 200.

Image information may be generated in accordance with receivedinformation distributed among a specific space using the communicationportion 290. For example, educational materials can be distributed amonga classroom and displayed to be used as a school book. Alternatively,materials transmitted among a conference room in a company can bereceived and displayed.

This embodiment can be combined with any of the other embodiments inthis specification as appropriate.

Embodiment 8

In this embodiment, a semiconductor device (memory device) that canretain stored data even when not powered and that has an unlimitednumber of write cycles, and a CPU including the semiconductor devicewill be described. The CPU described in this embodiment can be used forthe information processing device described in Embodiment 7, forexample.

<Memory Device>

An example of a semiconductor device (memory device) which can retainstored data even when not powered and which has an unlimited number ofwrite cycles is shown in FIGS. 27A to 27C. Note that FIG. 27B is acircuit diagram of the structure in FIG. 27A.

The semiconductor device illustrated in FIGS. 27A and 27B includes atransistor 3200 using a first semiconductor material, a transistor 3300using a second semiconductor material, and a capacitor 3400.

The first and second semiconductor materials preferably have differentenergy gaps. For example, the first semiconductor material can be asemiconductor material other than an oxide semiconductor (examples ofsuch a semiconductor material include silicon (including strainedsilicon), germanium, silicon germanium, silicon carbide, galliumarsenide, aluminum gallium arsenide, indium phosphide, gallium nitride,and an organic semiconductor), and the second semiconductor material canbe an oxide semiconductor. A transistor using a material other than anoxide semiconductor, such as single crystal silicon, can operate at highspeed easily. On the other hand, a transistor including an oxidesemiconductor has a low off-state current.

The transistor 3300 is a transistor in which a channel is formed in asemiconductor layer including an oxide semiconductor. Since theoff-state current of the transistor 3300 is small, stored data can beretained for a long period. In other words, power consumption can besufficiently reduced because a semiconductor memory device in whichrefresh operation is unnecessary or the frequency of refresh operationis extremely low can be provided.

In FIG. 27B, a first wiring 3001 is electrically connected to a sourceelectrode of the transistor 3200. A second wiring 3002 is electricallyconnected to a drain electrode of the transistor 3200. A third wiring3003 is electrically connected to one of a source electrode and a drainelectrode of the transistor 3300. A fourth wiring 3004 is electricallyconnected to a gate electrode of the transistor 3300. A gate electrodeof the transistor 3200 and the other of the source electrode and thedrain electrode of the transistor 3300 are electrically connected to oneelectrode of the capacitor 3400. A fifth wiring 3005 is electricallyconnected to the other electrode of the capacitor 3400.

The semiconductor device in FIG. 27A has a feature that the potential ofthe gate electrode of the transistor 3200 can be retained, and thusenables writing, retaining, and reading of data as follows.

Writing and retaining of data are described. First, the potential of thefourth wiring 3004 is set to a potential at which the transistor 3300 isturned on, so that the transistor 3300 is turned on. Accordingly, thepotential of the third wiring 3003 is supplied to the gate of thetransistor 3200 and the capacitor 3400. That is, a predetermined chargeis supplied to the gate electrode of the transistor 3200 (writing).Here, one of two kinds of charges providing different potential levels(hereinafter referred to as a low-level charge and a high-level charge)is supplied. After that, the potential of the fourth wiring 3004 is setto a potential at which the transistor 3300 is turned off, so that thetransistor 3300 is turned off. Thus, the charge supplied to the gateelectrode of the transistor 3200 is held (retaining).

Since the off-state current of the transistor 3300 is extremely small,the charge of the gate electrode of the transistor 3200 is retained fora long time.

Next, reading of data is described. An appropriate potential (a readingpotential) is supplied to the fifth wiring 3005 while a predeterminedpotential (a constant potential) is supplied to the first wiring 3001,whereby the potential of the second wiring 3002 varies depending on theamount of charge retained in the gate electrode of the transistor 3200.This is because in the case of using an n-channel transistor as thetransistor 3200, an apparent threshold voltage V_(th_H) at the time whenthe high-level charge is given to the gate electrode of the transistor3200 is lower than an apparent threshold voltage V_(th_L) at the timewhen the low-level charge is given to the gate electrode of thetransistor 3200. Here, an apparent threshold voltage refers to thepotential of the fifth wiring 3005 which is needed to turn on thetransistor 3200. Thus, the potential of the fifth wiring 3005 is set toa potential V₀ which is between V_(th_H) and V_(th_L), whereby chargesupplied to the gate electrode of the transistor 3200 can be determined.For example, in the case where the high-level charge is supplied to thegate electrode of the transistor 3200 in writing and the potential ofthe fifth wiring 3005 is V₀ (>V_(th_H)), the transistor 3200 is turnedon. On the other hand, in the case where the low-level charge issupplied to the gate electrode of the transistor 3200 in writing, evenwhen the potential of the fifth wiring 3005 is V₀ (V_(th_L)), thetransistor 3200 remains off. Thus, the data retained in the gateelectrode of the transistor 3200 can be read by determining thepotential of the second wiring 3002.

Note that in the case where memory cells are arrayed, it is necessarythat data of a desired memory cell is read. For example, the fifthwiring 3005 of memory cells from which data is not read may be suppliedwith a potential at which the transistor 3200 is turned off regardlessof the potential supplied to the gate electrode, that is, a potentiallower than V_(th_H), whereby only data of a desired memory cell can beread. Alternatively, the fifth wiring 3005 of the memory cells fromwhich data is not read may be supplied with a potential at which thetransistor 3200 is turned on regardless of the potential supplied to thegate electrode, that is, a potential higher than V_(th_L), whereby onlydata of a desired memory cell can be read.

The semiconductor device illustrated in FIG. 27C is different from thesemiconductor device illustrated in FIG. 27A in that the transistor 3200is not provided. Also in this case, writing and retaining operation ofdata can be performed in a manner similar to the semiconductor deviceillustrated in FIG. 27A.

Next, reading of data of the semiconductor device illustrated in FIG.27C is described. When the transistor 3300 is turned on, the thirdwiring 3003 which is in a floating state and the capacitor 3400 areelectrically connected to each other, and the charge is redistributedbetween the third wiring 3003 and the capacitor 3400. As a result, thepotential of the third wiring 3003 is changed. The amount of change inthe potential of the third wiring 3003 varies depending on the potentialof the one electrode of the capacitor 3400 (or the charge accumulated inthe capacitor 3400).

For example, the potential of the third wiring 3003 after the chargeredistribution is (C_(B)×V_(B0)+C×V)/(C_(B)+C), where V is the potentialof the one electrode of the capacitor 3400, C is the capacitance of thecapacitor 3400, CB is the capacitance component of the third wiring3003, and V_(B0) is the potential of the third wiring 3003 before thecharge redistribution. Thus, it can be found that, assuming that thememory cell is in either of two states in which the potential of the oneelectrode of the capacitor 3400 is V₁ and V₀ (V₁>V₀), the potential ofthe third wiring 3003 in the case of retaining the potential V₁(=(C_(B)×V_(B0)+C×V₁)/(C_(B)+C)) is higher than the potential of thethird wiring 3003 in the case of retaining the potential V₀(=(C_(B)×V_(B0)+C×V₀)/(C_(B)+C)).

Then, by comparing the potential of the third wiring 3003 with apredetermined potential, data can be read.

In this case, a transistor including the first semiconductor materialmay be used for a driver circuit for driving a memory cell, and atransistor including the second semiconductor material may be stackedover the driver circuit as the transistor 3300.

When including a transistor in which a channel formation region isformed using an oxide semiconductor and which has an extremely smalloff-state current, the semiconductor device described in this embodimentcan retain stored data for an extremely long time. In other words,refresh operation becomes unnecessary or the frequency of the refreshoperation can be extremely low, which leads to a sufficient reduction inpower consumption. Moreover, stored data can be retained for a long timeeven when power is not supplied (note that a potential is preferablyfixed).

Furthermore, in the semiconductor device described in this embodiment,high voltage is not needed for writing data and there is no problem ofdeterioration of elements. Unlike in a conventional nonvolatile memory,for example, it is not necessary to inject and extract electrons intoand from a floating gate; thus, a problem such as deterioration of agate insulating film is not caused. That is, the semiconductor devicedescribed in this embodiment does not have a limit on the number oftimes data can be rewritten, which is a problem of a conventionalnonvolatile memory, and the reliability thereof is drastically improved.Furthermore, data is written depending on the state of the transistor(on or off), whereby high-speed operation can be easily achieved.

The above memory device can also be used in an LSI such as a digitalsignal processor (DSP), a custom LSI, or a programmable logic device(PLD), in addition to a central processing unit (CPU), and a radiofrequency identification (RF-ID) tag, for example.

<CPU>

A CPU including the above memory device is described below.

FIG. 28 is a block diagram illustrating a configuration example of theCPU including the above memory device.

The CPU illustrated in FIG. 28 includes, over a substrate 1190, anarithmetic logic unit (ALU) 1191, an ALU controller 1192, an instructiondecoder 1193, an interrupt controller 1194, a timing controller 1195, aregister 1196, a register controller 1197, a bus interface (BUS I/F)1198, a rewritable ROM 1199, and a ROM interface (ROM I/F) 1189. Asemiconductor substrate, an SOI substrate, a glass substrate, or thelike is used as the substrate 1190. The ROM 1199 and the ROM interface1189 may be provided over a separate chip. Needless to say, the CPU inFIG. 28 is just an example in which the configuration is simplified, andan actual CPU may have a variety of configurations depending on theapplication. For example, the CPU may have the following configuration:a structure including the CPU illustrated in FIG. 28 or an arithmeticcircuit is considered as one core; a plurality of the cores areincluded; and the cores operate in parallel. The number of bits that theCPU can process in an internal arithmetic circuit or in a data bus canbe, for example, 8, 16, 32, or 64.

An instruction that is input to the CPU through the bus interface 1198is input to the instruction decoder 1193 and decoded therein, and then,input to the ALU controller 1192, the interrupt controller 1194, theregister controller 1197, and the timing controller 1195.

The ALU controller 1192, the interrupt controller 1194, the registercontroller 1197, and the timing controller 1195 conduct various controlsin accordance with the decoded instruction. Specifically, the ALUcontroller 1192 generates signals for controlling the operation of theALU 1191. While the CPU is executing a program, the interrupt controller1194 processes an interrupt request from an external input/output deviceor a peripheral circuit depending on its priority or a mask state. Theregister controller 1197 generates an address of the register 1196, andreads/writes data from/to the register 1196 depending on the state ofthe CPU.

The timing controller 1195 generates signals for controlling operationtimings of the ALU 1191, the ALU controller 1192, the instructiondecoder 1193, the interrupt controller 1194, and the register controller1197. For example, the timing controller 1195 includes an internal clockgenerator for generating an internal clock signal on the basis of areference clock signal, and supplies the internal clock signal to theabove circuits.

In the CPU illustrated in FIG. 28, a memory cell is provided in theregister 1196.

In the CPU illustrated in FIG. 28, the register controller 1197 selectsoperation of retaining data in the register 1196 in accordance with aninstruction from the ALU 1191. That is, the register controller 1197selects whether data is retained by a flip-flop or by a capacitor in thememory cell included in the register 1196. When data retaining by theflip-flop is selected, a power supply voltage is supplied to the memorycell in the register 1196. When data retaining by the capacitor isselected, the data is rewritten in the capacitor, and supply of thepower supply voltage to the memory cell in the register 1196 can bestopped.

FIG. 29 is an example of a circuit diagram of a memory element that canbe used for the register 1196. A memory element 1200 includes a circuit1201 in which stored data is volatile when power supply is stopped, acircuit 1202 in which stored data is nonvolatile even when power supplyis stopped, a switch 1203, a switch 1204, a logic element 1206, acapacitor 1207, and a circuit 1220 having a selecting function. Thecircuit 1202 includes a capacitor 1208, a transistor 1209, and atransistor 1210. Note that the memory element 1200 may further includeanother element such as a diode, a resistor, or an inductor, as needed.

Here, the above-described memory device can be used as the circuit 1202.When supply of a power supply voltage to the memory element 1200 isstopped, a ground potential (0 V) or a potential at which the transistor1209 in the circuit 1202 is turned off continues to be input to a gateof the transistor 1209. For example, the gate of the transistor 1209 isgrounded through a load such as a resistor.

Shown here is an example in which the switch 1203 is a transistor 1213having one conductivity type (e.g., an n-channel transistor) and theswitch 1204 is a transistor 1214 having a conductivity type opposite tothe one conductivity type (e.g., a p-channel transistor). A firstterminal of the switch 1203 corresponds to one of a source and a drainof the transistor 1213, a second terminal of the switch 1203 correspondsto the other of the source and the drain of the transistor 1213, andconduction or non-conduction between the first terminal and the secondterminal of the switch 1203 (i.e., the on/off state of the transistor1213) is selected by a control signal RD input to a gate of thetransistor 1213. A first terminal of the switch 1204 corresponds to oneof a source and a drain of the transistor 1214, a second terminal of theswitch 1204 corresponds to the other of the source and the drain of thetransistor 1214, and conduction or non-conduction between the firstterminal and the second terminal of the switch 1204 (i.e., the on/offstate of the transistor 1214) is selected by the control signal RD inputto a gate of the transistor 1214.

One of a source and a drain of the transistor 1209 is electricallyconnected to one of a pair of electrodes of the capacitor 1208 and agate of the transistor 1210. Here, the connection portion is referred toas a node M2. One of a source and a drain of the transistor 1210 iselectrically connected to a wiring that can supply a low power supplypotential (e.g., a GND line), and the other thereof is electricallyconnected to the first terminal of the switch 1203 (the one of thesource and the drain of the transistor 1213). The second terminal of theswitch 1203 (the other of the source and the drain of the transistor1213) is electrically connected to the first terminal of the switch 1204(the one of the source and the drain of the transistor 1214). The secondterminal of the switch 1204 (the other of the source and the drain ofthe transistor 1214) is electrically connected to a wiring that cansupply a power supply potential VDD. The second terminal of the switch1203 (the other of the source and the drain of the transistor 1213), thefirst terminal of the switch 1204 (the one of the source and the drainof the transistor 1214), an input terminal of the logic element 1206,and one of a pair of electrodes of the capacitor 1207 are electricallyconnected to each other. Here, the connection portion is referred to asa node M1. The other of the pair of electrodes of the capacitor 1207 canbe supplied with a constant potential. For example, the other of thepair of electrodes of the capacitor 1207 can be supplied with a lowpower supply potential (e.g., GND) or a high power supply potential(e.g., VDD). The other of the pair of electrodes of the capacitor 1207is electrically connected to the wiring that can supply a low powersupply potential (e.g., a GND line). The other of the pair of electrodesof the capacitor 1208 can be supplied with a constant potential. Forexample, the other of the pair of electrodes of the capacitor 1208 canbe supplied with a low power supply potential (e.g., GND) or a highpower supply potential (e.g., VDD). The other of the pair of electrodesof the capacitor 1208 is electrically connected to the wiring that cansupply a low power supply potential (e.g., a GND line).

The capacitor 1207 and the capacitor 1208 are not necessarily providedas long as the parasitic capacitance of the transistor, the wiring, orthe like is actively utilized.

A control signal WE is input to a first gate (first gate electrode) ofthe transistor 1209. As for each of the switch 1203 and the switch 1204,a conduction state or a non-conduction state between the first terminaland the second terminal is selected by the control signal RD that isdifferent from the control signal WE. When the first terminal and thesecond terminal of one of the switches are in the conduction state, thefirst terminal and the second terminal of the other of the switches arein the non-conduction state.

A signal corresponding to data retained in the circuit 1201 is input tothe other of the source and the drain of the transistor 1209. FIG. 29illustrates an example in which a signal output from the circuit 1201 isinput to the other of the source and the drain of the transistor 1209.The logic value of a signal output from the second terminal of theswitch 1203 (the other of the source and the drain of the transistor1213) is inverted by the logic element 1206, and the inverted signal isinput to the circuit 1201 through the circuit 1220.

In the example of FIG. 29, a signal output from the second terminal ofthe switch 1203 (the other of the source and the drain of the transistor1213) is input to the circuit 1201 through the logic element 1206 andthe circuit 1220; however, one embodiment of the present invention isnot limited thereto. The signal output from the second terminal of theswitch 1203 (the other of the source and the drain of the transistor1213) may be input to the circuit 1201 without its logic value beinginverted. For example, in the case where the circuit 1201 includes anode in which a signal obtained by inversion of the logic value of asignal input from the input terminal is retained, the signal output fromthe second terminal of the switch 1203 (the other of the source and thedrain of the transistor 1213) can be input to the node.

In FIG. 29, the transistors included in the memory element 1200 exceptfor the transistor 1209 can each be a transistor in which a channel isformed in a layer formed using a semiconductor other than an oxidesemiconductor or in the substrate 1190. For example, the transistor canbe a transistor whose channel is formed in a silicon layer or a siliconsubstrate. Alternatively, a transistor in which a channel is formed inan oxide semiconductor film can be used for all the transistors in thememory element 1200. Further alternatively, in the memory element 1200,a transistor in which a channel is formed in an oxide semiconductor filmcan be included besides the transistor 1209, and a transistor in which achannel is formed in a layer formed using a semiconductor other than anoxide semiconductor or the substrate 1190 can be used for the rest ofthe transistors.

As the circuit 1201 in FIG. 29, for example, a flip-flop circuit can beused. As the logic element 1206, for example, an inverter or a clockedinverter can be used.

In a period during which the memory element 1200 is not supplied withthe power supply voltage, the semiconductor device described in thisembodiment can retain data stored in the circuit 1201 by the capacitor1208 that is provided in the circuit 1202.

The off-state current of a transistor in which a channel is formed in anoxide semiconductor film is extremely small. For example, the off-statecurrent of a transistor in which a channel is formed in an oxidesemiconductor film is significantly smaller than that of a transistor inwhich a channel is formed in silicon having crystallinity. Thus, whenthe transistor in which a channel is formed in an oxide semiconductorfilm is used as the transistor 1209, a signal is retained in thecapacitor 1208 for a long time also in a period during which the powersupply voltage is not supplied to the memory element 1200. The memoryelement 1200 can accordingly retain the stored content (data) also in aperiod during which the supply of the power supply voltage is stopped.

Since the memory element performs pre-charge operation with the switch1203 and the switch 1204, the time required for the circuit 1201 toretain original data again after the supply of the power supply voltageis restarted can be shortened.

In the circuit 1202, a signal retained by the capacitor 1208 is input tothe gate of the transistor 1210. Thus, after supply of the power supplyvoltage to the memory element 1200 is restarted, the signal retained bythe capacitor 1208 can be converted into the one corresponding to thestate (the on state or the off state) of the transistor 1210 to be readfrom the circuit 1202. Consequently, an original signal can beaccurately read even when a potential corresponding to the signalretained by the capacitor 1208 changes to some degree.

By using the above-described memory element 1200 in a memory device suchas a register or a cache memory included in a processor, data in thememory device can be prevented from being lost owing to the stop of thesupply of the power supply voltage. Furthermore, shortly after thesupply of the power supply voltage is restarted, the memory device canbe returned to the same state as that before the power supply isstopped. Thus, the power supply can be stopped even for a short time inthe processor or one or a plurality of logic circuits included in theprocessor, resulting in lower power consumption.

Although the memory element 1200 is used in a CPU in this embodiment,the memory element 1200 can also be used in an LSI such as a digitalsignal processor (DSP), a custom LSI, or a programmable logic device(PLD), and a radio frequency identification (RF-ID).

At least part of this embodiment can be implemented in combination withany of the other embodiments described in this specification asappropriate.

Embodiment 9

In this embodiment, a display module and electronic devices whichinclude a reflective display device of one embodiment of the presentinvention will be described with reference to FIGS. 30A to 30H.

FIGS. 30A to 30G illustrate electronic devices. These electronic devicescan include a housing 5000, a display portion 5001, a speaker 5003, anLED lamp 5004, operation keys 5005 (including a power switch and anoperation switch), a connection terminal 5006, a sensor 5007 (a sensorhaving a function of measuring force, displacement, position, speed,acceleration, angular velocity, rotational frequency, distance, light,liquid, magnetism, temperature, chemical substance, sound, time,hardness, electric field, current, voltage, electric power, radiation,flow rate, humidity, gradient, oscillation, odor, or infrared ray), amicrophone 5008, and the like.

FIG. 30A illustrates a mobile computer which can include a switch 5009,an infrared port 5010, and the like in addition to the above components.FIG. 30B illustrates a portable image reproducing device (e.g., a DVDreproducing device) provided with a recording medium, and the portableimage reproducing device can include a second display portion 5002, arecording medium reading portion 5011, and the like in addition to theabove components. FIG. 30C illustrates a goggle-type display which caninclude the second display portion 5002, a support portion 5012, anearphone 5013, and the like in addition to the above components. FIG.30D illustrates a portable game console which can include the recordingmedium reading portion 5011 and the like in addition to the abovecomponents. FIG. 30E illustrates a digital camera with a televisionreception function, and the digital camera can include an antenna 5014,a shutter button 5015, an image receiving portion 5016, and the like inaddition to the above components. FIG. 30F illustrates a portable gameconsole which can include the second display portion 5002, the recordingmedium reading portion 5011, and the like in addition to the abovecomponents. FIG. 30G illustrates a portable television receiver whichcan include a charger 5017 capable of transmitting and receivingsignals, and the like in addition to the above components.

The electronic devices in FIGS. 30A to 30G can have a variety offunctions such as a function of displaying a variety of information(e.g., a still image, a moving image, and a text image) on the displayportion, a touch panel function, a function of displaying a calendar,date, time, and the like, a function of controlling processing with avariety of software (programs), a wireless communication function, afunction of being connected to a variety of computer networks with awireless communication function, a function of transmitting andreceiving a variety of data with a wireless communication function, anda function of reading out a program or data stored in a recording mediumand displaying it on the display portion. Furthermore, the electronicdevice including a plurality of display portions can have a function ofdisplaying image information mainly on one display portion whiledisplaying text information mainly on another display portion, afunction of displaying a three-dimensional image by displaying images ona plurality of display portions with a parallax taken into account, orthe like. Furthermore, the electronic device including an imagereceiving portion can have a function of shooting a still image, afunction of taking moving images, a function of automatically ormanually correcting a shot image, a function of storing a shot image ina recording medium (an external recording medium or a recording mediumincorporated in the camera), a function of displaying a shot image onthe display portion, or the like. Note that functions of the electronicdevices in FIGS. 30A to 30G are not limited thereto, and the electronicdevices can have a variety of functions.

FIG. 30H illustrates a smart watch, which includes a housing 7302, adisplay panel 7304, operation buttons 7311 and 7312, a connectionterminal 7313, a band 7321, a clasp 7322, and the like.

The display panel 7304 mounted in the housing 7302 serving as a bezelincludes a non-rectangular display region. The display panel 7304 mayhave a rectangular display region. The display panel 7304 can display anicon 7305 indicating time, another icon 7306, and the like.

The smart watch in FIG. 30H can have a variety of functions such as afunction of displaying a variety of information (e.g., a still image, amoving image, and a text image) on the display portion, a touch panelfunction, a function of displaying a calendar, date, time, and the like,a function of controlling processing with a variety of software(programs), a wireless communication function, a function of beingconnected to a variety of computer networks with a wirelesscommunication function, a function of transmitting and receiving avariety of data with a wireless communication function, and a functionof reading out a program or data stored in a recording medium anddisplaying it on the display portion.

The housing 7302 can include a speaker, a sensor (a sensor having afunction of measuring force, displacement, position, speed,acceleration, angular velocity, rotational frequency, distance, light,liquid, magnetism, temperature, chemical substance, sound, time,hardness, electric field, current, voltage, electric power, radiation,flow rate, humidity, gradient, oscillation, odor, or infrared rays), amicrophone, and the like. Note that the smart watch can be manufacturedusing the light-emitting element for the display panel 7304.

This embodiment can be combined with any of the other embodiments inthis specification as appropriate.

Example 1

In this example, a fabricated display panel of one embodiment of thepresent invention will be described with reference to FIGS. 31A1 to 31C.

FIGS. 31A to 31C are photos of the fabricated display panel displayingimages. FIGS. 31A1 to 31A3 and FIG. 31C are photos for showing thedisplay quality of the display panel when the first display element wasused. FIGS. 31B1 to 31B3 are photos for showing the display quality ofthe display panel when the second display element was used.

Table 1 shows the specifications of the fabricated display panel.

TABLE 1 Panel size 1.55 inch Effective pixels 320 × RGB (H) × 320 (V)Pixel size 29 μm (H) × 87 μm (V) Resolution 292 ppi First displayelement Reflective liquid crystal element (ECB mode) Second displayelement Organic EL element (Bottom emission) Pixel circuit LCD: 1 Tr + 1C EL: 2 Tr + 1 C Aperture ratio LCD: 69% EL: 3.9% Scan line drivercircuit incorporated Signal line driver circuit COF

A reflective liquid crystal element of an electrically controlledbirefringence (ECB) mode was used as the first display element includedin the fabricated display panel, which is one embodiment of the presentinvention. A white-light-emitting organic EL element was used as thesecond display element.

The fabricated display panel included a coloring layer having regionsoverlapping with the first display element and the second displayelement. Full-color display was performed utilizing light passingthrough the coloring layer.

<<Evaluation>>

The display panel made displays using the first display element in alight room equipped with a fluorescent lamp (see FIGS. 31A1 to 31A3).The display panel offered good full-color display using the reflectiveliquid crystal element.

In addition, using the first display element, the display panelperformed display outdoors in fine weather during the daytime (see FIG.31C). Even under such strong ambient light, the display panel offeredgood full-color display using the reflective liquid crystal element.

The display panel performed display in a dark place using the seconddisplay element (see FIGS. 31B1 to 31B3). The display panel offered goodfull-color display using the organic EL element.

In this specification and the like, for example, when it is explicitlydescribed that X and Y are connected, the case where X and Y areelectrically connected, the case where X and Y are functionallyconnected, and the case where X and Y are directly connected areincluded therein. Accordingly, another element may be interposed betweenelements having a connection relation shown in drawings and texts,without limiting to a predetermined connection relation, for example,the connection relation shown in the drawings and the texts.

Here, X and Y each denote an object (e.g., a device, an element, acircuit, a line, an electrode, a terminal, a conductive film, or alayer).

For example, in the case where X and Y are directly connected, anelement that enables electrical connection between X and Y (e.g., aswitch, a transistor, a capacitor, an inductor, a resistor, a diode, adisplay element, a light-emitting element, or a load) is not connectedbetween X and Y, and X and Y are connected without the element thatenables electrical connection between X and Y (e.g., a switch, atransistor, a capacitor, an inductor, a resistor, a diode, a displayelement, a light-emitting element, or a load) provided therebetween.

For example, in the case where X and Y are electrically connected, oneor more elements that enable electrical connection between X and Y(e.g., a switch, a transistor, a capacitor, an inductor, a resistor, adiode, a display element, a light-emitting element, or a load) can beconnected between X and Y. A switch is controlled to be on or off. Thatis, a switch is conducting or not conducting (is turned on or off) todetermine whether current flows therethrough or not. Alternatively, theswitch has a function of selecting and changing a current path. Notethat the case where X and Y are electrically connected includes the casewhere X and Y are directly connected.

For example, in the case where X and Y are functionally connected, oneor more circuits that enable functional connection between X and Y(e.g., a logic circuit such as an inverter, a NAND circuit, or a NORcircuit; a signal converter circuit such as a DA converter circuit, anAD converter circuit, or a gamma correction circuit; a potential levelconverter circuit such as a power source circuit (e.g., a step-upcircuit or a step-down circuit) or a level shifter circuit for changingthe potential level of a signal; a voltage source; a current source; aswitching circuit; an amplifier circuit such as a circuit that canincrease signal amplitude, the amount of current, or the like, anoperational amplifier, a differential amplifier circuit, a sourcefollower circuit, or a buffer circuit; a signal generation circuit; amemory circuit; and/or a control circuit) can be connected between X andY. Note that for example, in the case where a signal output from X istransmitted to Y even when another circuit is interposed between X andY, X and Y are functionally connected. Note that the case where X and Yare functionally connected includes the case where X and Y are directlyconnected and the case where X and Y are electrically connected.

Note that when it is explicitly described that X and Y are electricallyconnected, the case where X and Y are electrically connected (i.e., thecase where X and Y are connected with another element or another circuitprovided therebetween), the case where X and Y are functionallyconnected (i.e., the case where X and Y are functionally connected withanother circuit provided therebetween), and the case where X and Y aredirectly connected (i.e., the case where X and Y are connected withoutanother element or another circuit provided therebetween) are includedtherein. That is, in this specification and the like, the explicitdescription “X and Y are electrically connected” is the same as thedescription “X and Y are connected”.

For example, any of the following expressions can be used for the casewhere a source (or a first terminal or the like) of a transistor iselectrically connected to X through (or not through) Z1 and a drain (ora second terminal or the like) of the transistor is electricallyconnected to Y through (or not through) Z2, or the case where a source(or a first terminal or the like) of a transistor is directly connectedto one part of Z1 and another part of Z1 is directly connected to Xwhile a drain (or a second terminal or the like) of the transistor isdirectly connected to one part of Z2 and another part of Z2 is directlyconnected to Y.

Examples of the expressions include, “X, Y, a source (or a firstterminal or the like) of a transistor, and a drain (or a second terminalor the like) of the transistor are electrically connected to each other,and X, the source (or the first terminal or the like) of the transistor,the drain (or the second terminal or the like) of the transistor, and Yare electrically connected to each other in this order”, “a source (or afirst terminal or the like) of a transistor is electrically connected toX, a drain (or a second terminal or the like) of the transistor iselectrically connected to Y, and X, the source (or the first terminal orthe like) of the transistor, the drain (or the second terminal or thelike) of the transistor, and Y are electrically connected to each otherin this order”, and “X is electrically connected to Y through a source(or a first terminal or the like) and a drain (or a second terminal orthe like) of a transistor, and X, the source (or the first terminal orthe like) of the transistor, the drain (or the second terminal or thelike) of the transistor, and Y are provided to be connected in thisorder”. When the connection order in a circuit structure is defined byan expression similar to the above examples, a source (or a firstterminal or the like) and a drain (or a second terminal or the like) ofa transistor can be distinguished from each other to specify thetechnical scope.

Other examples of the expressions include, “a source (or a firstterminal or the like) of a transistor is electrically connected to Xthrough at least a first connection path, the first connection path doesnot include a second connection path, the second connection path is apath between the source (or the first terminal or the like) of thetransistor and a drain (or a second terminal or the like) of thetransistor, Z1 is on the first connection path, the drain (or the secondterminal or the like) of the transistor is electrically connected to Ythrough at least a third connection path, the third connection path doesnot include the second connection path, and Z2 is on the thirdconnection path”. Another example of the expression is “a source (or afirst terminal or the like) of a transistor is electrically connected toX at least with a first connection path through Z1, the first connectionpath does not include a second connection path, the second connectionpath includes a connection path through which the transistor isprovided, a drain (or a second terminal or the like) of the transistoris electrically connected to Y at least with a third connection paththrough Z2, and the third connection path does not include the secondconnection path”. Still another example of the expression is “a source(or a first terminal or the like) of a transistor is electricallyconnected to X through at least Z1 on a first electrical path, the firstelectrical path does not include a second electrical path, the secondelectrical path is an electrical path from the source (or the firstterminal or the like) of the transistor to a drain (or a second terminalor the like) of the transistor, the drain (or the second terminal or thelike) of the transistor is electrically connected to Y through at leastZ2 on a third electrical path, the third electrical path does notinclude a fourth electrical path, and the fourth electrical path is anelectrical path from the drain (or the second terminal or the like) ofthe transistor to the source (or the first terminal or the like) of thetransistor”. When the connection path in a circuit structure is definedby an expression similar to the above examples, a source (or a firstterminal or the like) and a drain (or a second terminal or the like) ofa transistor can be distinguished from each other to specify thetechnical scope.

Note that these expressions are examples and there is no limitation onthe expressions. Here, X, Y, Z1, and Z2 each denote an object (e.g., adevice, an element, a circuit, a wiring, an electrode, a terminal, aconductive film, and a layer).

Even when independent components are electrically connected to eachother in a circuit diagram, one component has functions of a pluralityof components in some cases. For example, when part of a wiring alsofunctions as an electrode, one conductive film functions as the wiringand the electrode. Thus, “electrical connection” in this specificationincludes in its category such a case where one conductive film hasfunctions of a plurality of components.

EXPLANATION OF REFERENCE

-   -   ACF1: conductive material, ACF2: conductive material, AF1:        alignment film, AF2: alignment film, ANO: wiring, C1: capacitor,        C2: capacitor, CF1: coloring film, CF2: coloring film, CP:        conductive member, CS: wiring, G: scan line, G1: scan line, G2:        scan line, GD: driver circuit, SD: driver circuit, GDA: driver        circuit, GDB: driver circuit, KB1: structure, KB2: structure,        KB3: structure, M: transistor, MB: transistor, MD: transistor,        MDB: transistor, M1: node, M2: node, P1: positional information,        P2: information, SW1: switch, SW2: switch, T1: time, T2: time,        T3: time, T4: time, T5: time, T6: time, V: image data, V0:        potential, V1: potential, VCOM1: wiring, VCOM2: wiring, VDD:        power supply potential, FPC1: flexible printed circuit board,        FPC2: flexible printed circuit board, PIC1: image data, PIC2:        image data, PIC3: image data, PIC4: image data, 100: transistor,        102: substrate, 104: conductive film, 106: insulating film, 107:        insulating film, 108: oxide semiconductor film, 108 a: oxide        semiconductor film, 108 b: oxide semiconductor film, 108 c:        oxide semiconductor film, 112 a: conductive film, 112 b:        conductive film, 114: insulating film, 116: insulating film,        118: insulating film, 120 a: conductive film, 120 b: conductive        film, 150: transistor, 200: data processor, 210: arithmetic        device, 211: arithmetic portion, 212: memory portion, 214:        transmission path, 215: input/output interface, 220:        input/output device, 230: display portion, 230B: display        portion, 231: display region, 232: pixel, 235EL: display        element, 235LC: display element, 240: input portion, 250: sensor        portion, 290: communication portion, 501A: insulating film,        501B: insulating film, 501C: insulating film, 501D: insulating        film, 504: conductive film, 504C: contact, 505: bonding layer,        506: insulating film, 508: semiconductor film, 510: substrate,        510W: separation film, 511: wiring, 512A: conductive film, 512B:        conductive film, 516: insulating film, 518: insulating film,        520: functional layer, 519: terminal, 519B: terminal, 519D:        terminal, 520D: functional layer, 521A: insulating film, 521B:        insulating film, 524: conductive film, 528: insulating film,        550: display element, 550B: display element, 551: conductive        film, 552: conductive film, 553: layer containing a        light-emitting organic compound, 553B: layer containing a        light-emitting organic compound, 570: substrate, 570B:        insulating film, 591: contact, 592: contact, 593: contact, 700:        display panel, 700B: display panel, 700C: display panel, 700D:        display panel, 700E: display panel, 700F: display panel, 702:        pixel, 704: conductive film, 704C: contact, 705: sealant, 719:        terminal, 730: pixel circuit, 750: display element, 751:        conductive film, 751T: conductive film, 751H: opening, 752:        conductive film, 752C: conductive film, 753: layer containing a        liquid crystal material, 753T: layer containing electronic ink,        770: substrate, 770P: optical film, 771: insulating film, 800:        input/output device, 801: upper cover, 802: lower cover, 803:        FPC, 804: touch sensor, 805: FPC, 806: display panel, 809:        frame, 810: driver circuit, 811: battery, 1189: ROM interface,        1190: substrate, 1191: ALU, 1192: ALU controller, 1193:        instruction decoder, 1194: interrupt controller, 1195: timing        controller, 1196: register, 1197: register controller, 1198: bus        interface, 1199: ROM, 1200: memory element, 1201: circuit, 1202:        circuit, 1203: switch, 1204: switch, 1206: logic element, 1207:        capacitor, 1208: capacitor, 1209: transistor, 1210: transistor,        1213: transistor, 1214: transistor, 1220: circuit, 3001: wiring,        3002: wiring, 3003: wiring, 3004: wiring, 3005: wiring, 3200:        transistor, 3300: transistor, 3400: capacitor, 5000: housing,        5001: display portion, 5002: display portion, 5003: speaker,        5004: LED lamp, 5005: operation key, 5006: connection terminal,        5007: sensor, 5008: microphone, 5009: switch, 5010: infrared        port, 5011: recording medium reading portion, 5012: support        portion, 5013: earphone, 5014: antenna, 5015: shutter button,        5016: image receiving portion, 5017: charger, 7302: housing,        7304: display panel, 7305: icon, 7306: icon, 7311: operation        button, 7312: operation button, 7313: connection terminal, 7321:        band, 7322: clasp.

This application is based on Japanese Patent Application serial no.2015-081519 filed with Japan Patent Office on Apr. 13, 2015, JapanesePatent Application serial no. 2015-115638 filed with Japan Patent Officeon Jun. 8, 2015, and Japanese Patent Application serial no. 2015-150202filed with Japan Patent Office on Jul. 30, 2015, the entire contents ofwhich are hereby incorporated by reference.

The invention claimed is:
 1. A display panel comprising a pixel and aterminal; the pixel comprising: a first insulating film; a first contactportion in a first opening in the first insulating film; a pixel circuitelectrically connected to the first contact portion; a second contactportion electrically connected to the pixel circuit; a first displayelement electrically connected to the first contact portion; and asecond display element electrically connected to the second contactportion; wherein the first insulating film is between the first displayelement and the second display element, wherein the first displayelement includes a first conductive film having a second opening,wherein the first conductive film is capable of reflecting incidentlight, wherein the first display element is capable of controlling theintensity of the reflected light, wherein the second display elementincludes a region overlapping with the second opening, wherein theregion overlapping with the second opening emits light toward the secondopening, and wherein the terminal is electrically connected to the pixelcircuit.
 2. The display panel according to claim 1, wherein the pixelcircuit includes a switching element.
 3. The display panel according toclaim 1, wherein the pixel circuit includes a transistor, and whereinthe transistor includes an oxide semiconductor.
 4. The display panelaccording to claim 1, wherein the pixel includes a second insulatingfilm in contact with the first conductive film.
 5. The display panelaccording to claim 1, wherein the first display element includes a layercontaining a liquid crystal material and the first conductive film and asecond conductive film which are provided to control the alignment ofthe liquid crystal material, and wherein the first conductive film iselectrically connected to the first contact portion.
 6. The displaypanel according to claim 1, wherein the second display element includesa third conductive film, a fourth conductive film including a regionoverlapping with the third conductive film, and a layer containing alight-emitting organic compound between the third conductive film andthe fourth conductive film, wherein the third conductive film iselectrically connected to the second contact portion, and wherein thethird conductive film transmits light.
 7. The display panel according toclaim 1, wherein the first display element is configured to reflectexternal light, and wherein the ratio of the total area of the secondopening provided in the first conductive film to that of a portion ofthe first conductive film other than the second opening is more than orequal to 0.052 and less than or equal to 0.6.
 8. The display panelaccording to claim 1, wherein the first conductive film includes aregion embedded in the first insulating film.
 9. The display panelaccording to claim 1, wherein the light emitted toward the secondopening is extracted from a display surface of the display panel throughthe second opening.
 10. A display panel comprising a pixel and aterminal; the pixel comprising: a first insulating film; a secondinsulating film in contact with the first insulating film; a firstcontact portion in a first opening in the first insulating film and thesecond insulating film; a pixel circuit electrically connected to thefirst contact portion; a second contact portion electrically connectedto the pixel circuit; a first display element electrically connected tothe first contact portion; and a second display element electricallyconnected to the second contact portion; wherein the first insulatingfilm is between the first display element and the second displayelement, wherein the first display element includes a first conductivefilm having a second opening, wherein the first conductive film iscapable of reflecting incident light, wherein the first display elementis capable of controlling the intensity of the reflected light, whereinthe second display element includes a region overlapping with the secondopening, wherein the region overlapping with the second opening emitslight toward the second opening, wherein the terminal is electricallyconnected to the pixel circuit, wherein the pixel circuit includes afirst transistor electrically connected to the first contact portion anda second transistor electrically connected to the second contactportion, and wherein the second insulating film is in contact with thefirst transistor and the second transistor.
 11. The display panelaccording to claim 10, wherein the first transistor and the secondtransistor each includes an oxide semiconductor.
 12. The display panelaccording to claim 10, wherein the pixel includes a third insulatingfilm, and wherein the first conductive film is between the secondinsulating film and the third insulating film.
 13. The display panelaccording to claim 10, wherein the first display element includes alayer containing a liquid crystal material and the first conductive filmand a second conductive film which are provided to control the alignmentof the liquid crystal material, and wherein the first conductive film iselectrically connected to the first contact portion.
 14. The displaypanel according to claim 10, wherein the second display element includesa third conductive film, a fourth conductive film including a regionoverlapping with the third conductive film, and a layer containing alight-emitting organic compound between the third conductive film andthe fourth conductive film, wherein the third conductive film iselectrically connected to the second contact portion, and wherein thethird conductive film transmits light.
 15. The display panel accordingto claim 10, wherein the first display element is configured to reflectexternal light, and wherein the ratio of the total area of the secondopening provided in the first conductive film to that of a portion ofthe first conductive film other than the second opening is more than orequal to 0.052 and less than or equal to 0.6.
 16. The display panelaccording to claim 10, wherein the first conductive film includes aregion embedded in the first insulating film.
 17. The display panelaccording to claim 10, wherein the light emitted toward the secondopening is extracted from a display surface of the display panel throughthe second opening.